Guide: How to find a good PSU

citay

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The four main points are:

1) Look for an 80 PLUS Gold specification or better. 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 (because there's less power going to waste), require less airflow (which makes less noise), and last longer.



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 these for example.

I usually recommend the following PSU models because i can vouch for them:
Best mid-range: be quiet! Pure Power 11 (CM/FM) or Seasonic Core GM
Best upper mid-range: be quiet! Straight Power 11 (Platinum) or Seasonic Focus GX/PX
Best high-end: be quiet! Dark Power 12 (Pro) or Seasonic TX

Of course there are also many good models from other brands. Note that each brand sells a variety of models with sometimes vastly different quality, so always look at specific PSU models.
For example, EVGA are known to sell a lot of PSU models with all kinds of quality, from the very bad (EVGA W1) to the halfway decent or mediocre (EVGA BQ, GD, GQ) to the very good (EVGA G6).

What to avoid completely:
- Noname PSU brands in general. Just stick to well-known PSU brands like Seasonic, be quiet!, Corsair, 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 (=below Bronze). 80 PLUS Bronze is the minimum for a halfway decent PSU. But some no-name brands even use fake 80+ certificates.
- PSUs with a price that seems too cheap for their specifications (from Chinese shops for example).
- PSU brands that are only sold in a specific region, like NOX, Acbel, Artis, Pichau, Redragon etc.
- Cheap cases that come with a PSU inside.

The required total PSU wattage depends mostly on the CPU and the graphics card, they are the most power-hungry components. Again, 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 (you never want the PSU to work at the limit all the time).

Examples:
B550 motherboard + Ryzen 5600X + RAM + SSD: ~150W max, 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 + RAM + SSD: 250+W max, GeForce RTX 3080 or Radeon 6900 XT: 300+W max, and you also need more headroom, so get a quality a 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 most important.


Now, a more detailed explanation 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. 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 decent quality components cost more money, and almost every component is important in some way. So 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.

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 and it was popular a decade and more ago, but nowadays it's just not suitable. 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.

Apart from the internal design, of course the PSU makers can also cheap out the components in general. Here we come to another 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 so-called "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.

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 often gradual. Meaning, it won't go up in a puff of smoke, it will cause instabilities at first, or even things like file corruption.

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.

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

A good review lab will have such equipment available for PSU testing. Again, i 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.
 
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