PSUs 101: A Detailed Look Into Power Supplies

The objective of this article is to provide detailed information about the most crucial part of a personal computer (PC) system, its power supply unit. Follow us on this journey into PSU territory and we promise that you will gain valuable knowledge.

For those of you who know nothing about PSUs, today we're taking it from the top. The abbreviation PSU stands for power supply unit, and in this article, we assume that it is also an SMPS (switching mode power supply), since in modern PCs only SMPS units are used.

You can think of the PSU as the heart of a PC; it is the most significant part of the system since it feeds power to the other components, including the CPU, graphics card, hard drive, SSD and so on. If the PSU fails, it affects all of the other pieces. And in some cases, a malfunction of the PSU can damage other components as well, especially if the PSU is of low quality with inefficient protection features. Unfortunately, this is something many builders ignore. Instead of choosing an adequate PSU for their systems, users typically acquire all of the other components first, using leftover funds for the power supply purchase. If you've made this mistake, we are sure that after reading this article you will change your PC building strategy. However, this article is not just intended for novice users and goes beyond the basics of PSUs, providing valuable information to experienced enthusiasts as well.

In the following sections we will provide an easy-to-follow explanation of the switch power conversion. We will also make a brief reference to the most significant electronic components currently used not only in PSU manufacturing, but also in every modern electronics device. Through the following pages you will learn the basic concepts of inductors, capacitors, resistors, transistors and diodes in order to better understand PSU components. Next, the main context of switching power conversion will be explained and a brief description of the various stages that compose a PSU will be made. Afterward, we will make a brief reference to some switching regulator topologies, which are commonly used nowadays. Some of you might not be aware of this, but a PSU's cooling fan is usually the first part to stop working, at least in good-quality PSUs, so we will dedicate some time to discussing cooling fans as well. Next, we'll spend some time on protection features, and finally we will take a look at ATX, EPS and 80 PLUS specifications. 

This is going to be an informative journey through electronics, and when you finish reading this article, we are confident that you will have gained valuable knowledge that will help you to better understand the "Look Inside" pages in our PSU reviews. In addition, you will be able to judge the technical specifications of a PSU by yourself.

In the following section, we briefly describe the most significant electronic parts that are used in PSUs, including inductors, transformers, capacitors, resistors, transistors and diodes. This essential knowledge will help you when we analyze the internal parts of an SMPS, especially if you don't have an electronics background.

MORE: How We Test Power Supplies
MORE: 
Who's Who In Power Supplies, 2014: Brands Vs. Manufacturers
MORE: 
All Power Supply Articles
MORE: 
Power Supplies in the Forums

Create a new thread in the US Reviews comments forum about this subject
This thread is closed for comments
42 comments
    Your comment
  • In your list of top-tier capacitor manufacturers you missed out on some of the better american and european manufacturers, while these may not be used on many consumer-grade power supplies they are definitely top-tier and if you were to find them you would be happy. I suggest the addition of at least:
    Cornell Dubilier (USA)
    Illinois Capacitor (Now owned my Cornell Dubilier)
    Kemet Corporation (USA)
    ELNA (Japan)
    EPCOS (TDK company) (Germany)
    Vishay (USA)
    Würth Elektronik (Germany)
    4
  • Thank you very much for the list you provided. I am aware of almost all cap brands that you mentioned but unfortunately so far I found none of them inside a desktop/consumer grade PSU. I will think about it however (and also make a research on these cap brands), if I should include them as well inside my list.
    2
  • 1903369 said:
    Thank you very much for the list you provided. I am aware of almost all cap brands that you mentioned but unfortunately so far I found none of them inside a desktop/consumer grade PSU.

    There is a very high probability you have seen PSUs with several Kemet capacitors in them. You never noticed them simply because SMD capacitors are too small to carry logos, brand name or even value designations.

    The other brands are mostly found in specialty applications such as lab instruments, industrial machines and high-end audio.
    2
  • very interesting read. more in depth than i need to know yet for the most part understandable and with careful reading it did not leave me confused.

    nice article.
    2
  • I only read 2/3 of it, but it's a good article.

    I basically have committed PC heresy with my cx600m. However I think that I'm in the clear with my 65w CPU and 145w CPU. I'd bet my total power draw is actually below 300w, the supposed highest efficiency point of a PSU.

    As a gamer, not a professional, I think it is better to get low power parts, and get a higher rating than you need, rather than get high power parts and high quality PSUs.

    Additionally, if you compare power consumption of a typical system from today to one from 5 years ago, power draw is considerably lower, with the exception of certain graphics cards. *cough* 390x *cough*
    0
  • I decided to sign up at Tom's forum, and the only reason was to state how excellent is Aris's article!!!
    Thanks Aris for this very useful article on behalf of us all who want to learn the basic knowledge for PSUs.
    Haven't finished it yet, but i'm very anxious for it !!!
    6
  • Very nice article!!! You made me remember my college physics courses lol
    3
  • I'm glad there are people dedicated to this but I'm not. I can't even read all of the chapter titles in this article. I disagree with the importance you place on this and all of the references you made to this being crucial knowledge.

    PSU and MB are insignificant to me and I can blindly pick one by reviewing user comments from newegg in about 5 min, and it will last for years. For less than $100 each I'm set for nearly a decade.

    CPU and gfx card now that affects fps and is over $1000, actually the most important part to me.
    -12
  • 481739 said:
    I'm glad there are people dedicated to this but I'm not. I can't even read all of the chapter titles in this article. I disagree with the importance you place on this and all of the references you made to this being crucial knowledge. PSU and MB are insignificant to me and I can blindly pick one by reviewing user comments from newegg in about 5 min, and it will last for years. For less than $100 each I'm set for nearly a decade. CPU and gfx card now that affects fps and is over $1000, actually the most important part to me.


    I heartily dissagree, user are not the best way to judge reliability, and a bad powersupply is at fult most of the time there is a hardware issue. Further a power supply should last more than one system build, and in general I keep mine for a decade at a time at least. So an investment in a good power supply is not a waste, and a bad one will kill that precious $1000 GPU or CPU. The demo dart power supply on the motherboard is a similar story, however in general they are of higher quality than a cheap mains supply.
    7
  • 125865 said:
    1903369 said:
    Thank you very much for the list you provided. I am aware of almost all cap brands that you mentioned but unfortunately so far I found none of them inside a desktop/consumer grade PSU.
    There is a very high probability you have seen PSUs with several Kemet capacitors in them. You never noticed them simply because SMD capacitors are too small to carry logos, brand name or even value designations. The other brands are mostly found in specialty applications such as lab instruments, industrial machines and high-end audio.


    As well as SMT ceramic capacitors, Kemet makes through hole aluminium electrolytic capacitors. These are of high quality, though not as well known as their SMT capacitors. They also make high quality polymer SMT capacitors that are used as bulk capacitors on the power distribution circuitry on laptops and other devices.
    0
  • A concise and informative article, written with remarkable effort. As an instrumentation engineer I found it enchanting. Thank you Mr. Aris.
    1
  • That's a monster of a PSU. But very very overpriced! I would much rather just buy a Seasonic at that price!
    0
  • Great writeup.
    0
  • Quote:
    In your list of top-tier capacitor manufacturers you missed out on some of the better american and european manufacturers, while these may not be used on many consumer-grade power supplies they are definitely top-tier and if you were to find them you would be happy. I suggest the addition of at least: Cornell Dubilier (USA) Illinois Capacitor (Now owned my Cornell Dubilier) Kemet Corporation (USA) ELNA (Japan) EPCOS (TDK company) (Germany) Vishay (USA) Würth Elektronik (Germany)


    Decide to include them in the article for reference and to show also that besides Japanese caps they are also some good US and German brands. Thanks again for your input!
    0
  • I was told there be no math questions...
    .
    LOL
    .
    Seriously though, very complete article
    0
  • Quote:
    I'm glad there are people dedicated to this but I'm not. I can't even read all of the chapter titles in this article. I disagree with the importance you place on this and all of the references you made to this being crucial knowledge. PSU and MB are insignificant to me and I can blindly pick one by reviewing user comments from newegg in about 5 min, and it will last for years. For less than $100 each I'm set for nearly a decade. CPU and gfx card now that affects fps and is over $1000, actually the most important part to me.



    You probably buy cheap hard drives, too.

    Enjoy your ticking time bomb. Because a cheap PSU and cheap motherboard is the quickest and surest way to a total system failure.
    3
  • Great article !!
    Toms should write more like this..
    1
  • Quote:
    One or more bridge rectifiers fully correct the AC power stream after it passes the EMI/transient filter.


    You mean rectifies. A bridge rectifier converts the AC voltage into DC voltage.
    The name bridge, comes from being a bridge of four (power) diodes. ( image: Source: Play Hookey)
    1
  • Finally a PSU article! :P
    0
  • I had it rectify and not "correct" but the proof editors changed it. Sorry will fix it ASAP. Of course they rectify and this is why they are called bridge rectifiers after all.
    1