What Is A Computer Power Supply?

Recently, I had an older computer in my house stop working on me. I had expected it to die on me years ago, but I was surprised to discover that it wasn’t a computer component that died, but rather my power supply. When I pulled the older model out of the computer I stood there looking at it and I had to ask myself what this electrical brick actually is. As a computer enthusiast I know what it does on a basic level and why, but not any real details. So I decided to do a little research.

So what is a computer power supply? A computer power supply unit (Commonly known as PSU) provides power to computer components by converting AC power from your wall outlet to low-voltage regulated DC power for your computer. Modern PCs will use ATX specification, which is the modern standard switch-mode power supplies most desktop computers conform to.

There are a few other types of power supplies, but to most desktop computers, those are irrelevant. ATX power supplies have been the standard for a very long time and aren’t going anywhere.


Important Terms to Know

Like all computer components, power supplies have a lot going on with them. For someone that is new to this, there are some terms that are commonly thrown around that might be a little confusing. Whether you’re simply looking up information on power supplies, or are looking to shop for a new one, there’s certainly some terms worth knowing:

  • PSU – Short for Power Supply Unit. This is the full name for a computer power supply and is usually shortened to PSU when being referenced as it’s just easier to say.
  • AC – Short for alternating current. This is a form of power that can alternate in direction and is the power that will be delivered from your typical electrical outlet.
  • DC – Short for direct current. Unlike AC, DC delivers a constant current that cannot change direction. DC currents have an easier to regulate voltage than AC and are ideal for sensitive electrical components in a computer.
  • ATX Motherboard Connector – This is the largest power cable on your power supply and has 20 or 24 pins. This connects to the motherboard to provide it with power. Sometimes the 24 pin connector is split between a 20 and 4 pin connectors that plug into slots right next to each other.
  • 4 Pin Peripheral – These are smaller connectors that typically plug into your disk drives to provide them with power.
  • 6 Pin Connector – These power cables are usually connected to PCI Express graphics cards to provide them with power.
  • SATA Connector – Otherwise known as Serial ATA connectors. These power cables connect to your hard drives to provide them with power.
  • Non-Modular PSU – This is an older form of power supply that is being phased out. They are called non-modular because they come out of the box with all the possible power cables already attached without an option to remove them.
  • Modular PSU – The opposite of a non-modular power supply. These newer generation power supplies allow you plug in and use only the amount of power cables you need, avoiding an unwanted bundle of cables that go nowhere.

These are not all the terms you may encounter when you’re looking up information on PSUs, but with this core knowledge, you should have a much easier time knowing what people are referring to when they say these words!

A Closer Look at Power Supplies

As mentioned before, there is only one main standard specification that all PSUs conform to in the modern age, and that’s ATX. ATX was invented by Intel in 1995 and revolutionized the power supply scene by standardizing everything.

Before ATX, there was XT and AT. All you really need to know about these power supplies these days is that these were most proprietary PSUs that difficult to remove from your computer and sometimes even soldered into your case. This was essentially the Wild West of the power supply days!

Modern power supplies all use ATX because not only did it simplify the PSU industry, but it also allowed greater competition with innovations that improved quality and lowered prices. Allowing for greater flexibility with personal computers and allowing enthusiasts to more easily order parts for their systems they intended to build.

These days, you don’t have to do a whole lot of extra research when you’re buying a power supply. The best things you can do are:

  • Ensure you’re buying from a reputable brand. You pay for quality, and knock off brands are never a good idea.
  • Buy more wattage than you think you’ll need to ensure the health of your system. This is typically measured by the power rating of the PSU.
  • Pay attention to the efficiency rating of the power supply.

What’s efficiency rating and 80 Plus? Simply put, modern power supplies are becoming more and more efficient with their power usage as technology improves. The industry standard is 80% or higher efficiency. 80 Plus is a voluntary certification program used to measure how efficient a power supply is. I’ll supply a quick graph:


Without over complicating anything. The higher rated the 80 Plus label on the PSU, the better the power supply generally is. Don’t stray from this rule and you’re golden!


How Does a Computer Power Supply Work

A PSU is an interesting computer component because it’s both a complicated piece of machinery, but the concept of what it does is very simple.

I will be the first to admit that I am not an electrical engineer, so I won’t be able to go into too much detail about how the actual electrical parts of a power supply work. I can, however, give you a good idea of how it functions.

Note – Because PSUs are complicated pieces of electrical equipment, it’s not advised to open or work on them. They are typically not serviceable by the average computer user. For your safety, please take your power supply to a professional to be worked on it if requires it. Otherwise, replacing them are simple and hassle free.

Computer power supplies operate on a basic principle. They take AC power from the electrical outlet on your wall and then convert it to a highly regulated direct current (DC) that will power your internal components. DC has a much lower voltage than AC when regulated, and it’s for this reason that the power supply exists. PC parts run on very low voltage and as a result, would never be able to take the high voltage AC directly from the outlet.

Once the power has been converted to DC, it can then be funneled to the rest of your computer components. This is where all the various pin connector cables come into play. Each PC part will have a different sized pin connector plugged into them from the power supply. Some, like your motherboard, will use a giant 20 or 24 pin connector. Others, like a fan or graphics card, will use 4 or 6 pin connectors.

If you’re replacing parts in your computer, be sure to check their user manuals to ensure you’re using the correct pin connectors to power them. Typically, though, it will be fairly obvious, as it will simply be the one you unplugged to take the first component out of your case.


Common Concerns About Power Supplies

While power supplies are as efficient as ever these days and are extremely easy to buy with the simplified rating systems they have, there are still some concerns that we should keep in mind:

  • If you’re installing a power supply, ensure that none of its wires are near fans. A fan catching a wire is a quick way to kill a computer.
  • PSUs can still suffer from power surges even in this modern era. If needed, use a surge protector to extend the life of your power supply and computer.
  • If your computer case has a PSU shroud, install the power supply face down to avoiding choking off the intake fan.
  • Don’t overload your PSU with too many power hungry components. If your computer is shutting down randomly or won’t turn on at all, this may be a cause.

If you’re installing a power supply and are wanting to read more about whether your should install if facing up or now, I’ve written an article on that here and it may be of use to you!

Installing Power Supply Face Down

Amping Up the Power (Conclusion)

Computer Power Supplies are a curious thing. As said before, they’re complicated on the inside, but simple on the outside. There’re many layers of understanding when it comes to PSUs and even I can’t say I know everything. Thankfully, with all the innovations that have taken place to drive simplicity, you don’t need to know everything to be confident with power supplies.

If you have any questions of comments, please be sure to leave them below and I’ll do my best to get back to you directly!


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