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The four main points are:
1) Look for an 80 PLUS Gold specification (or better, if you wish). The price increase over 80 PLUS Bronze isn't big anymore, and 80 PLUS Gold is quite a lot more efficient.
Not only will this save money on the electricity bill, it will also run cooler (less power going to waste), require less airflow (which makes less noise), and last longer.
Also, with the step from Bronze to Gold efficiency, the PSU makers need to use more modern and sophisticated technology to reach that higher efficiency, which happens to improve just about every other aspect of the PSU as well. That is the real reason to prefer a Gold model for anything other than a low-end system nowadays.
2) Look for a long warranty period (ideally 5 years or more), implying the manufacturer's confidence in the product.
3) Check the PSU tier list, which gives a rough indication of many PSU models' quality. Ideal is Tier A or B.
4) Optional, but recommended: Read a proper review of the PSU model you may want to buy.
For example, when you build a silent system, you also want a silent PSU. But there are some good PSU models (80 PLUS Gold and long warranty) that might still make a bit more noise than you want. So by reading a review, you can make sure that there are no dealbreakers. However, don't rely on amateur reviews where they are using just a PC with no test equipment. PSU reviews have to be done by people with knowledge and using the proper equipment, like in this example.
Always look at specific PSU models. There are certain PSU brands like "be quiet!" or Seasonic which tend to keep a decent standard across most of their PSU models. But a lot of brands also offer a variety of models with vastly different quality, with the cheapest ones being almost dangerously bad. For example, EVGA sell PSU models ranging from the very bad (EVGA W1) to the halfway decent or mediocre (EVGA BQ, GD, GQ) to the very good (EVGA G6). More often than not, the price of the PSU directly translates to its quality.
As i'll explain later, there aren't really any good deals with PSUs, instead, you pretty much get what you pay for. So i recommend spending a bit more and getting a PSU model that can last way longer, all the while running more quietly, running more efficiently, providing cleaner power to the components, and so on. Even for an office PC, i would get a quality PSU, but the rated wattage can obviously be quite low then.
For the best cheap PSU, or should i say "most acceptable" cheap PSU, you should look at what's available for your budget, and first filter the models with help of the PSU Tier List. Disregard anything worse than Tier C as well as anything from the "what to avoid" list further below in this post, then try to find the best model within your price range. Disregard PSUs with only 80PLUS White or no 80PLUS certification. Prefer PSUs from well-known PSU brands, and see if you can find a review that will list a specific model's pros and cons.
The minimum amount of money you have to spend on a PSU for it not to be complete trash starts around 40-50 EUR/USD. In some countries, PSUs may be more expensive, so the minimum amount you have to spend might start at 60 EUR/USD. And this is just for a PSU that will not cause problems after a relatively short time or harm your components when it fails! So financially, it makes no sense to go for the cheapest PSU models, they will cause problems after some time and then you have to buy a new one again. While you may have saved money at first, you will spend more money way sooner than with a good PSU model.
There is just no way to save a lot of money on PSUs. With the CPU or RAM, you can get a slower model and the result is not severe, just the performance will be lower. But when you go too cheap on a PSU, you basically put all your other hardware at risk, among many other other negative effects like bad efficiency, "dirty" output voltages that go out of spec under load, instability, things like that. Out of all the components to go too cheap on, the PSU is probably the worst one, it will always come back to haunt you later. I like to call an overly cheap PSU somewhat of a ticking timebomb.
What to avoid completely / red flags:
- Noname PSUs. Just stick to well-known PSU brands like Seasonic, be quiet!, Corsair etc., and find a good model from them (not all of their models are necessarily good).
- PSU models you can't find on the PSU tier list, or that are worse than Tier C. But even Tier C isn't ideal and has to be avoided for a nicer system, go for Tier A or B then.
- PSUs without 80 PLUS certification, or with just 80 PLUS White, or 80 PLUS Bronze "EU" (230V only). The full 80 PLUS Bronze certification is the minimum for a halfway decent PSU. Some no-name models even have made-up certificates like "82+". Just stick to a model that's high enough on the PSU Tier List and it will be 80 PLUS Bronze or better.
- PSUs with a price that seems too cheap for their specifications (from Chinese shops for example). There are no "great deals" with PSUs. If it's very cheap, it's also bad quality.
- PSU brands that are only sold in a specific region, like NOX, Acbel, Artis, Pichau, Redragon..., because they are often bad quality and can't compete on the worldwide market.
- Cheap cases that come with a PSU included inside. The low price guarantees that such a PSU is of terrible quality.
And finally, avoid PSU brands that have completely ruined their reputation, like Aerocool, Aresgame and Gamemax. They are known for "review samples manipulation" and "post-review design downgrades". This means that they send out a nice PSU (a so-called "golden sample") for the purpose of being reviewed, but the PSU that they eventually sell to the public will use cheaper and worse components, or even leave out components, and is not of the quality that was shown in the review.
And they might also submit such a golden sample PSU for the 80PLUS efficiency certificate, of course it achieves the certificate, but then they sell a worse PSU with the exact same model name to the public and keep the sticker with the 80PLUS certificate on it (which isn't valid for that new model anymore). The PSU they sell to the public ends up being borderline dangerous for your hardware in the end, and can easily fail.
PSU authority Jon Gerow aka "JonnyGuru" (now head of PSU R&D at Corsair) had this to say about an AeroCool PSU, for example:
When a manufacturer does this, like Aerocool, Aresgame and Gamemax have done, they are not to be trusted whatsoever, because they have no integrity as a company.
The last point is further made clear when watching this video about Gamemax's blatant plagiarism: They don't care about anything.
How many Watts?
The required total PSU wattage depends mostly on the CPU and the graphics card, as they are by far the most power-hungry components. It's good to read some CPU/GPU reviews to get a rough idea how much power those components will need under load, add it all up, and then get a suitable PSU with a bit of headroom (because you never want the PSU to work at the limit all the time).
Examples:
B550 motherboard + Ryzen 5600X = ~150W, Radeon 6600 or GeForce 3050: ~150W, and to have a bit of headroom, you should look at a quality 450W PSU or higher.
Z690 motherboard + Core i7-12700K = >250W, GeForce RTX 3080 or Radeon 6900 XT: >300W, and you also need more headroom, so get a quality 750W PSU or higher.
The emphasis here is on "quality". A good PSU model with less wattage is better than a bad one with more wattage.
A higher rated wattage doesn't hurt, but the PSU quality is the most important factor. If the quality is not there, an inflated wattage rating won't make it any better.
What differentiates a good PSU from a bad one?
First off, you might ask yourself, why is there even a guide on how to find a good PSU? After all, the PC seems to work fine even with a "bad" PSU.
Only when the PC doesn't want to turn on anymore, it could be a reason to replace the PSU, right?
Well, it's more complicated. The main thing with PSUs is, it is not a simple case of "on=works" and "off=broken". It's a complex piece of electronics which transforms the 230V or 115V mains power (depending on your country) into 12V, 5V and 3.3V for the PC to use. There can be a number of things wrong with the quality of the output voltages which are not immediately obvious.
In cheap/bad PSUs, there will be some cost-saving going on, which can make the PSU one of the first things (if not the first) to slowly cause problems in a PC. While cheap doesn't always equate to bad, there's a strong correlation with PSUs, because almost every component is important in some way. And components with a decent quality cost a certain amount of money.
So how come that some PSUs cost so much less than others at the same rated wattage? What are the cost-saving tricks with PSUs and how do they impact the quality?
There are three common ways for the PSU brand to save money. They are often used in combination:
1) Using a simpler (more outdated and less efficient) internal design which requires less components.
2) Using cheaper, lower-quality components.
3) Leaving out certain components.
The first potential problem with a cheap PSU lies in its internal design. The cheaper a PSU model has to be, the more outdated of an internal design they tend to use. Often, they tend to settle on a so-called "group-regulated" design for the cheap models, which has too much of an emphasis on the minor rails (5V/3.3V). With almost all power being pulled over the 12V rail nowadays, the other voltages will drop considerably under load with such a design. That group-regulated design is cheaper, because it requires less components than a more advanced design. It was common a decade or more ago, but nowadays it's just not suitable anymore. It can't handle cross-load with the majority of power draw from 12V, which is exactly what happens with modern hardware. Modern CPUs and graphics cards can also cause considerable so-called "transient loads", short (but high) peaks/bursts of power draw which PSUs with a group-regulated design are ill-equipped to handle. But even with a slightly more advanced design, there are ways to use less components, for example using a half-bridge vs. a full-bridge design and so on. The cheaper and more outdated the internal PSU design, the less efficient it will be (wasting more power into heat instead of being able to supply the power to your hardware).
The biggest step up in quality comes with 80PLUS Gold-rated PSUs, because the PSU makers need to use a better so-called topology to reach that Gold efficiency level. That almost automatically leads to better load regulation / voltage stability, better cross-load behaviour, better transient response, lower voltage ripple etc. And of course less power going to waste in the form of heat, which leads to lower temperatures inside, which leads to the electrolytic capacitors lasting longer, as well as lower noise levels (since they don't have to rely on an aggressive fan profile to keep the capacitors cool enough).
Apart from the internal design, of course the PSU makers can also cheap out the components in general. Here we come to another very common problem of cheap PSUs: The capacitor selection. Capacitors are components that can buffer electricity and filter/smooth the output voltages. They are important to reduce the "voltage ripple" and provide stable, clean voltages to the components attached to the PSU. There are distinct differences in quality and longevity between certain makers of capacitors (or caps for short), and even within the product range of each capacitor brand.
For one, the operating lifetime of a capacitor depends a lot on the ambient temperature, especially with electrolytic capacitors which have a fluid inside them. Caps have different maximum temperature ratings, either 85°C or 105°C, obviously the latter tends to last longer inside a warm place like a PSU. But the different brands of capacitors and even their individual product ranges make more of a difference. The caps all have a different reputation, depending on how well they held up in the past (especially in PSUs). There are some (usually Chinese/Taiwanese) brands with a not-so-good reputation like CapXon for example, and then there are some - usually Japanese - brands with a good reputation like Panasonic or Nippon Chemicon. Historically, the latter have survived well past the warranty of the PSU, while the cheaper brands depend a lot on higher airflow within the PSU, and tend to perhaps still fail soon after the warranty ends. Finally, in some places, so-called solid caps can be used, but they are more expensive and mostly used in high-end PSUs.
In my experience, PSUs are consistently among the first component to fail in a PC, in large part owed to capacitors not being able to do their job properly anymore.
Sometimes one is greeted by this upon inspecting the failing PSU: Bulged or leaking capacitors.
Other times it might not be so obvious, but the caps might still not filter the voltages very well anymore. The problem with less filtered output voltages is that all the connected components are put under more stress and might also degrade earlier than expected. This is an often underestimated factor when using a cheap PSU: The "dirtier" the output voltages are, the more the attached hardware has to "pick up the slack", and now their filtering capacitors and circuitry are under more stress and aging faster!
It's also important where the capacitors are placed inside the PSU. In the picture above, they are directly next to a MOSFET (switching/amplifying transistor), a component that can get very hot and is actually screwed to a heatsink. So caps that are in a hot, cramped corner of the PSU are also a recipe for early failure, especially with budget caps rated for 85°C. The following photo shows the inside of a Thermaltake Smart BX1 RGB, where the cheap secondary capacitors from ChengX (green) are leaning against the chokes (ferrite cores with windings), which warm up under load and negatively affect the lifetime of the heat-sensitive capacitors:
Here's a measurement from a Deepcool PF650 with an almost identical setup to the photo above, the capacitors really get subjected to a lot of heat in there and they can age in record time:
Of course, there can be a lot of other negatives in a cheap PSU than just the capacitors, for example a low overall efficiency. But when a cheap PSU starts to fail, it's often because of the capacitors, and the failure is usually gradual. Meaning, it won't go up in a puff of smoke, it will cause instabilities at first, or even things like file corruption, because the capacitors don't do their job properly anymore.
The PSU makers tend to adjust their warranty period accordingly, meaning they often won't give more than two or three years of warranty for their cheaper PSU models. In other words, that was the timeframe they deemed comfortable for the quality of capacitors they used and their placement (how much they heat up, since that will shorten their lifespan). When capacitors age, they can't properly do their part in supplying clean power to the components anymore, and can't handle transient (sudden) loads or sustained full load very well. One cheap way for the PSU makers to prevent premature capacitor aging is to use an aggressive fan curve, which will force a lot of air over the components to remove the heat more quickly. Of course that has the downside of being rather noisy.
The final cost-saving trick in PSUs is simple: Leaving out components altogether. This can be a theme throughout the whole PSU: Less input filtering components (which makes it more susceptible to interference), less components that would improve efficiency (which makes it waste more power into heat), less components that handle power (which makes it weaker under load), and even leaving out some protection circuits (which makes it dangerous to itself and your other hardware).
So, building a cheap, but reasonably good and quiet PSU is not easy at all. With five or more years of warranty on a reasonably quiet PSU, the capacitors can't be the cheapest quality, otherwise the manufacturer wouldn't be comfortable with that warranty period. That's why the warranty is one of the good indicators of PSU quality. Basically, a long enough warranty weeds out a lot of the PSUs that will fail too early and thus would be a waste of money anyway. It's better to spend a bit more and have a better, more efficient, longer-lasting PSU that will continue to output clean voltages for years.
The issue with assessing the PSU's output quality, or to detect PSU aging: To properly test it, it would need to run on a programmable power source and power meter (for example a CHROMA test station, to create exactly specified loads). Then the PSU's outputs would have to be observed under load with an oscilloscope. Here are photos of such a setup:
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma01.jpg
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma02.jpg
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma03.jpg
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma04.jpg
Here is the equipment that is used by the PSU testing legend Aris from HWBusters:
A good review lab will have special equipment available for PSU testing. Again, if they just use a normal PC to review a PSU, it's not a proper PSU review.
The PSU is the foundation of the entire system. The PSU has to match the other hardware, not just in wattage, but in quality as well. A budget PSU will not be outputting very clean voltages under load, especially not after a couple years of use. If you're building anything other than a cheap office PC and using a bit nicer and/or more powerful components, then those components would be subjected to unnecessary stress with a cheap PSU, not to mention the questionable long-term reliability of that setup. So the PSU, the foundation, it has to be solid for whatever PC is built on top of that.
ATX 3.0 / PCIe 5.0 necessary or not?
The newest NVIDIA GeForce 4000-series high-end graphics cards have a new 12VHPWR (12V High Power) connector, which requires a special cable. Only few new PSU models include a native cable for that (so that no adapters from several 8-pin PCIe power cables needed). Those PSUs are also touted as ATX 3.0 / PCIe 5.0 compatible, which mostly means that they have high tolerance for so-called transients - short bursts of very high power draw - in order to deal with a high-end GPU.
My favourite of those new PSUs, the be quiet! Dark Power 13, is not cheap, but then again, it's 80PLUS Titanium certified. The FSP Hydro Ti Pro is another nice high-end option. Looking at cheaper models, be quiet! have the new Straight Power 12 and Pure Power 12 M available, other notable ATX 3.0 models at the moment are the MSI MPG A850G PCIE5 (and other wattages) or the Thermaltake ToughPower GF3 ATX 3.0, and of course, more such PSU models are on their way.
Some brands like Corsair, Seasonic and indeed be quiet! offer a native ATX12HPWR cable seperately, for use with their existing high-wattage PSUs. Because many conventional high-end, high-wattage PSUs should have no problem with the GeForce 4090. While that GPU's power draw is crazy high, the transients are kept under control (better than on the GeForce 3000-series). As long as the PSU is sufficient for the combined power draw under load, those GPUs should not trip the OCP (OverCurrent Protection) of the PSU. So an ATX 3.0-spec PSU is not absolutely necessary, a good "normal" PSU will also do. But for better future-proofing, the ATX 3.0 spec becomes more and more attractive as new such PSU models are released.
My other guides:
RAM explained: Why two modules are better than four / single- vs. dual-rank / stability testing
Guide: How to set good power limits in the BIOS and reduce the CPU power draw
Guide: How to set up a fan curve in the BIOS
Someone asked me if they can thank me for my work by sending me something via Paypal: Yes, that's possible, just write me a message and i'll tell you my Paypal
1) Look for an 80 PLUS Gold specification (or better, if you wish). The price increase over 80 PLUS Bronze isn't big anymore, and 80 PLUS Gold is quite a lot more efficient.
Not only will this save money on the electricity bill, it will also run cooler (less power going to waste), require less airflow (which makes less noise), and last longer.
Also, with the step from Bronze to Gold efficiency, the PSU makers need to use more modern and sophisticated technology to reach that higher efficiency, which happens to improve just about every other aspect of the PSU as well. That is the real reason to prefer a Gold model for anything other than a low-end system nowadays.
2) Look for a long warranty period (ideally 5 years or more), implying the manufacturer's confidence in the product.
3) Check the PSU tier list, which gives a rough indication of many PSU models' quality. Ideal is Tier A or B.
4) Optional, but recommended: Read a proper review of the PSU model you may want to buy.
For example, when you build a silent system, you also want a silent PSU. But there are some good PSU models (80 PLUS Gold and long warranty) that might still make a bit more noise than you want. So by reading a review, you can make sure that there are no dealbreakers. However, don't rely on amateur reviews where they are using just a PC with no test equipment. PSU reviews have to be done by people with knowledge and using the proper equipment, like in this example.
Always look at specific PSU models. There are certain PSU brands like "be quiet!" or Seasonic which tend to keep a decent standard across most of their PSU models. But a lot of brands also offer a variety of models with vastly different quality, with the cheapest ones being almost dangerously bad. For example, EVGA sell PSU models ranging from the very bad (EVGA W1) to the halfway decent or mediocre (EVGA BQ, GD, GQ) to the very good (EVGA G6). More often than not, the price of the PSU directly translates to its quality.
As i'll explain later, there aren't really any good deals with PSUs, instead, you pretty much get what you pay for. So i recommend spending a bit more and getting a PSU model that can last way longer, all the while running more quietly, running more efficiently, providing cleaner power to the components, and so on. Even for an office PC, i would get a quality PSU, but the rated wattage can obviously be quite low then.
For the best cheap PSU, or should i say "most acceptable" cheap PSU, you should look at what's available for your budget, and first filter the models with help of the PSU Tier List. Disregard anything worse than Tier C as well as anything from the "what to avoid" list further below in this post, then try to find the best model within your price range. Disregard PSUs with only 80PLUS White or no 80PLUS certification. Prefer PSUs from well-known PSU brands, and see if you can find a review that will list a specific model's pros and cons.
The minimum amount of money you have to spend on a PSU for it not to be complete trash starts around 40-50 EUR/USD. In some countries, PSUs may be more expensive, so the minimum amount you have to spend might start at 60 EUR/USD. And this is just for a PSU that will not cause problems after a relatively short time or harm your components when it fails! So financially, it makes no sense to go for the cheapest PSU models, they will cause problems after some time and then you have to buy a new one again. While you may have saved money at first, you will spend more money way sooner than with a good PSU model.
There is just no way to save a lot of money on PSUs. With the CPU or RAM, you can get a slower model and the result is not severe, just the performance will be lower. But when you go too cheap on a PSU, you basically put all your other hardware at risk, among many other other negative effects like bad efficiency, "dirty" output voltages that go out of spec under load, instability, things like that. Out of all the components to go too cheap on, the PSU is probably the worst one, it will always come back to haunt you later. I like to call an overly cheap PSU somewhat of a ticking timebomb.
What to avoid completely / red flags:
- Noname PSUs. Just stick to well-known PSU brands like Seasonic, be quiet!, Corsair etc., and find a good model from them (not all of their models are necessarily good).
- PSU models you can't find on the PSU tier list, or that are worse than Tier C. But even Tier C isn't ideal and has to be avoided for a nicer system, go for Tier A or B then.
- PSUs without 80 PLUS certification, or with just 80 PLUS White, or 80 PLUS Bronze "EU" (230V only). The full 80 PLUS Bronze certification is the minimum for a halfway decent PSU. Some no-name models even have made-up certificates like "82+". Just stick to a model that's high enough on the PSU Tier List and it will be 80 PLUS Bronze or better.
- PSUs with a price that seems too cheap for their specifications (from Chinese shops for example). There are no "great deals" with PSUs. If it's very cheap, it's also bad quality.
- PSU brands that are only sold in a specific region, like NOX, Acbel, Artis, Pichau, Redragon..., because they are often bad quality and can't compete on the worldwide market.
- Cheap cases that come with a PSU included inside. The low price guarantees that such a PSU is of terrible quality.
And finally, avoid PSU brands that have completely ruined their reputation, like Aerocool, Aresgame and Gamemax. They are known for "review samples manipulation" and "post-review design downgrades". This means that they send out a nice PSU (a so-called "golden sample") for the purpose of being reviewed, but the PSU that they eventually sell to the public will use cheaper and worse components, or even leave out components, and is not of the quality that was shown in the review.
And they might also submit such a golden sample PSU for the 80PLUS efficiency certificate, of course it achieves the certificate, but then they sell a worse PSU with the exact same model name to the public and keep the sticker with the 80PLUS certificate on it (which isn't valid for that new model anymore). The PSU they sell to the public ends up being borderline dangerous for your hardware in the end, and can easily fail.
PSU authority Jon Gerow aka "JonnyGuru" (now head of PSU R&D at Corsair) had this to say about an AeroCool PSU, for example:
When a manufacturer does this, like Aerocool, Aresgame and Gamemax have done, they are not to be trusted whatsoever, because they have no integrity as a company.
The last point is further made clear when watching this video about Gamemax's blatant plagiarism: They don't care about anything.
How many Watts?
The required total PSU wattage depends mostly on the CPU and the graphics card, as they are by far the most power-hungry components. It's good to read some CPU/GPU reviews to get a rough idea how much power those components will need under load, add it all up, and then get a suitable PSU with a bit of headroom (because you never want the PSU to work at the limit all the time).
Examples:
B550 motherboard + Ryzen 5600X = ~150W, Radeon 6600 or GeForce 3050: ~150W, and to have a bit of headroom, you should look at a quality 450W PSU or higher.
Z690 motherboard + Core i7-12700K = >250W, GeForce RTX 3080 or Radeon 6900 XT: >300W, and you also need more headroom, so get a quality 750W PSU or higher.
The emphasis here is on "quality". A good PSU model with less wattage is better than a bad one with more wattage.
A higher rated wattage doesn't hurt, but the PSU quality is the most important factor. If the quality is not there, an inflated wattage rating won't make it any better.
What differentiates a good PSU from a bad one?
First off, you might ask yourself, why is there even a guide on how to find a good PSU? After all, the PC seems to work fine even with a "bad" PSU.
Only when the PC doesn't want to turn on anymore, it could be a reason to replace the PSU, right?
Well, it's more complicated. The main thing with PSUs is, it is not a simple case of "on=works" and "off=broken". It's a complex piece of electronics which transforms the 230V or 115V mains power (depending on your country) into 12V, 5V and 3.3V for the PC to use. There can be a number of things wrong with the quality of the output voltages which are not immediately obvious.
In cheap/bad PSUs, there will be some cost-saving going on, which can make the PSU one of the first things (if not the first) to slowly cause problems in a PC. While cheap doesn't always equate to bad, there's a strong correlation with PSUs, because almost every component is important in some way. And components with a decent quality cost a certain amount of money.
So how come that some PSUs cost so much less than others at the same rated wattage? What are the cost-saving tricks with PSUs and how do they impact the quality?
There are three common ways for the PSU brand to save money. They are often used in combination:
1) Using a simpler (more outdated and less efficient) internal design which requires less components.
2) Using cheaper, lower-quality components.
3) Leaving out certain components.
The first potential problem with a cheap PSU lies in its internal design. The cheaper a PSU model has to be, the more outdated of an internal design they tend to use. Often, they tend to settle on a so-called "group-regulated" design for the cheap models, which has too much of an emphasis on the minor rails (5V/3.3V). With almost all power being pulled over the 12V rail nowadays, the other voltages will drop considerably under load with such a design. That group-regulated design is cheaper, because it requires less components than a more advanced design. It was common a decade or more ago, but nowadays it's just not suitable anymore. It can't handle cross-load with the majority of power draw from 12V, which is exactly what happens with modern hardware. Modern CPUs and graphics cards can also cause considerable so-called "transient loads", short (but high) peaks/bursts of power draw which PSUs with a group-regulated design are ill-equipped to handle. But even with a slightly more advanced design, there are ways to use less components, for example using a half-bridge vs. a full-bridge design and so on. The cheaper and more outdated the internal PSU design, the less efficient it will be (wasting more power into heat instead of being able to supply the power to your hardware).
The biggest step up in quality comes with 80PLUS Gold-rated PSUs, because the PSU makers need to use a better so-called topology to reach that Gold efficiency level. That almost automatically leads to better load regulation / voltage stability, better cross-load behaviour, better transient response, lower voltage ripple etc. And of course less power going to waste in the form of heat, which leads to lower temperatures inside, which leads to the electrolytic capacitors lasting longer, as well as lower noise levels (since they don't have to rely on an aggressive fan profile to keep the capacitors cool enough).
Apart from the internal design, of course the PSU makers can also cheap out the components in general. Here we come to another very common problem of cheap PSUs: The capacitor selection. Capacitors are components that can buffer electricity and filter/smooth the output voltages. They are important to reduce the "voltage ripple" and provide stable, clean voltages to the components attached to the PSU. There are distinct differences in quality and longevity between certain makers of capacitors (or caps for short), and even within the product range of each capacitor brand.
For one, the operating lifetime of a capacitor depends a lot on the ambient temperature, especially with electrolytic capacitors which have a fluid inside them. Caps have different maximum temperature ratings, either 85°C or 105°C, obviously the latter tends to last longer inside a warm place like a PSU. But the different brands of capacitors and even their individual product ranges make more of a difference. The caps all have a different reputation, depending on how well they held up in the past (especially in PSUs). There are some (usually Chinese/Taiwanese) brands with a not-so-good reputation like CapXon for example, and then there are some - usually Japanese - brands with a good reputation like Panasonic or Nippon Chemicon. Historically, the latter have survived well past the warranty of the PSU, while the cheaper brands depend a lot on higher airflow within the PSU, and tend to perhaps still fail soon after the warranty ends. Finally, in some places, so-called solid caps can be used, but they are more expensive and mostly used in high-end PSUs.
In my experience, PSUs are consistently among the first component to fail in a PC, in large part owed to capacitors not being able to do their job properly anymore.
Sometimes one is greeted by this upon inspecting the failing PSU: Bulged or leaking capacitors.
Other times it might not be so obvious, but the caps might still not filter the voltages very well anymore. The problem with less filtered output voltages is that all the connected components are put under more stress and might also degrade earlier than expected. This is an often underestimated factor when using a cheap PSU: The "dirtier" the output voltages are, the more the attached hardware has to "pick up the slack", and now their filtering capacitors and circuitry are under more stress and aging faster!
It's also important where the capacitors are placed inside the PSU. In the picture above, they are directly next to a MOSFET (switching/amplifying transistor), a component that can get very hot and is actually screwed to a heatsink. So caps that are in a hot, cramped corner of the PSU are also a recipe for early failure, especially with budget caps rated for 85°C. The following photo shows the inside of a Thermaltake Smart BX1 RGB, where the cheap secondary capacitors from ChengX (green) are leaning against the chokes (ferrite cores with windings), which warm up under load and negatively affect the lifetime of the heat-sensitive capacitors:
Here's a measurement from a Deepcool PF650 with an almost identical setup to the photo above, the capacitors really get subjected to a lot of heat in there and they can age in record time:
Of course, there can be a lot of other negatives in a cheap PSU than just the capacitors, for example a low overall efficiency. But when a cheap PSU starts to fail, it's often because of the capacitors, and the failure is usually gradual. Meaning, it won't go up in a puff of smoke, it will cause instabilities at first, or even things like file corruption, because the capacitors don't do their job properly anymore.
The PSU makers tend to adjust their warranty period accordingly, meaning they often won't give more than two or three years of warranty for their cheaper PSU models. In other words, that was the timeframe they deemed comfortable for the quality of capacitors they used and their placement (how much they heat up, since that will shorten their lifespan). When capacitors age, they can't properly do their part in supplying clean power to the components anymore, and can't handle transient (sudden) loads or sustained full load very well. One cheap way for the PSU makers to prevent premature capacitor aging is to use an aggressive fan curve, which will force a lot of air over the components to remove the heat more quickly. Of course that has the downside of being rather noisy.
The final cost-saving trick in PSUs is simple: Leaving out components altogether. This can be a theme throughout the whole PSU: Less input filtering components (which makes it more susceptible to interference), less components that would improve efficiency (which makes it waste more power into heat), less components that handle power (which makes it weaker under load), and even leaving out some protection circuits (which makes it dangerous to itself and your other hardware).
So, building a cheap, but reasonably good and quiet PSU is not easy at all. With five or more years of warranty on a reasonably quiet PSU, the capacitors can't be the cheapest quality, otherwise the manufacturer wouldn't be comfortable with that warranty period. That's why the warranty is one of the good indicators of PSU quality. Basically, a long enough warranty weeds out a lot of the PSUs that will fail too early and thus would be a waste of money anyway. It's better to spend a bit more and have a better, more efficient, longer-lasting PSU that will continue to output clean voltages for years.
The issue with assessing the PSU's output quality, or to detect PSU aging: To properly test it, it would need to run on a programmable power source and power meter (for example a CHROMA test station, to create exactly specified loads). Then the PSU's outputs would have to be observed under load with an oscilloscope. Here are photos of such a setup:
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma01.jpg
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma02.jpg
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma03.jpg
https://www.hardwareluxx.de/images/stories/galleries/reviews/nt-roundup-chroma-april12/chroma04.jpg
Here is the equipment that is used by the PSU testing legend Aris from HWBusters:
A good review lab will have special equipment available for PSU testing. Again, if they just use a normal PC to review a PSU, it's not a proper PSU review.
The PSU is the foundation of the entire system. The PSU has to match the other hardware, not just in wattage, but in quality as well. A budget PSU will not be outputting very clean voltages under load, especially not after a couple years of use. If you're building anything other than a cheap office PC and using a bit nicer and/or more powerful components, then those components would be subjected to unnecessary stress with a cheap PSU, not to mention the questionable long-term reliability of that setup. So the PSU, the foundation, it has to be solid for whatever PC is built on top of that.
ATX 3.0 / PCIe 5.0 necessary or not?
The newest NVIDIA GeForce 4000-series high-end graphics cards have a new 12VHPWR (12V High Power) connector, which requires a special cable. Only few new PSU models include a native cable for that (so that no adapters from several 8-pin PCIe power cables needed). Those PSUs are also touted as ATX 3.0 / PCIe 5.0 compatible, which mostly means that they have high tolerance for so-called transients - short bursts of very high power draw - in order to deal with a high-end GPU.
My favourite of those new PSUs, the be quiet! Dark Power 13, is not cheap, but then again, it's 80PLUS Titanium certified. The FSP Hydro Ti Pro is another nice high-end option. Looking at cheaper models, be quiet! have the new Straight Power 12 and Pure Power 12 M available, other notable ATX 3.0 models at the moment are the MSI MPG A850G PCIE5 (and other wattages) or the Thermaltake ToughPower GF3 ATX 3.0, and of course, more such PSU models are on their way.
Some brands like Corsair, Seasonic and indeed be quiet! offer a native ATX12HPWR cable seperately, for use with their existing high-wattage PSUs. Because many conventional high-end, high-wattage PSUs should have no problem with the GeForce 4090. While that GPU's power draw is crazy high, the transients are kept under control (better than on the GeForce 3000-series). As long as the PSU is sufficient for the combined power draw under load, those GPUs should not trip the OCP (OverCurrent Protection) of the PSU. So an ATX 3.0-spec PSU is not absolutely necessary, a good "normal" PSU will also do. But for better future-proofing, the ATX 3.0 spec becomes more and more attractive as new such PSU models are released.
My other guides:
RAM explained: Why two modules are better than four / single- vs. dual-rank / stability testing
Guide: How to set good power limits in the BIOS and reduce the CPU power draw
Guide: How to set up a fan curve in the BIOS
Someone asked me if they can thank me for my work by sending me something via Paypal: Yes, that's possible, just write me a message and i'll tell you my Paypal
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