A power supply unit is the hardware that converts the power provided by an outlet into usable power for the many components inside the computer case.
It converts the AC power from the wall outlet to the DC power needed by the computer components. It also regulates overheating by controlling the voltage, which may vary automatically or manually depending on the power supply.
The power supply is a critical component because the rest of the internal hardware cannot function without it. Motherboards, cases, and power supplies all come in different sizes, called form factors. All three must be compatible to work properly.
CoolMax, CORSAIR and Ultra are the most popular manufacturers of PSU (Power Supply Unit) power supply units, but most are included in the computer purchase, so you can only deal with the manufacturer when replacing the PSU.
PSUs are generally not user-serviceable. For your safety, never turn on the power unit.
Description of the power supply unit
The power supply unit is mounted on the rear of the chassis. If you follow the computer's power cord from the wall, you'll find it connected to the back of the power supply. Its back is usually the only part of the unit that most people see. There's also a fan opening on the back that lets air out the back of the computer case.
The side of the PSU facing the outside of the case has a male three-prong port into which the power cord connected to the power supply plugs. There is also usually a power switch and a supply voltage switch.
A large bundle of colored wires runs from the other side of the power supply into the computer. The connectors on each end of the wire connect to the various components inside the computer, powering them. Some are specifically designed to plug into your motherboard, while others have connectors for fans, floppy drives, hard drives, optical drives, and even some high-powered video cards.
Power supplies are rated in wattage to show how much power they can provide to the computer. Since every computer part requires a certain amount of power to function properly, it's important to have a PSU that can provide the proper amount of power. The very handy Cooler Master Supply Calculator tool can help you determine how much you need.
ATX and ATX12V power supply
ATX and ATX12V are important configuration specifications to differentiate when dealing with power supplies. For most people, these apparent differences simply have to do with the physical connection headers on the motherboard. Choosing one over the other depends on the type of motherboard being used.
The latest standard ATX12V v2.4 has been used since 2013. Motherboards using ATX12V 2.x use a 24-pin connector. ATX motherboards use 20-pin connectors.
One situation where pin count comes into play is when deciding whether a particular power supply will work with your system. ATX12V compatible power supplies, although they have 24 pins, can actually be used on ATX motherboards that have 20 pin connectors. The four remaining, unused pins will just come out of the connector. If your computer case has the space, this is a totally doable setup.
However, this doesn't work the other way around. If you have an ATX power supply and therefore have a 20 pin connector, it won't work with new motherboards that require all 24 pins to be connected. The spec adds an extra four pins to provide additional power through the 12V rail, so a 20-pin PSU won't provide enough power to run this kind of board.
Note: ATX is also a term used to describe the size of a motherboard.
Another difference between ATX12V and ATX power supplies is the power connectors they offer. The ATX12V standard (since version 2.0) requires a 15-pin SATA power connector. If you need to use a SATA device, but the PSU doesn't have a SATA power connector, you'll need a Molex 4-pin to SATA 15-pin adapter.
Another difference between ATX and ATX12V is the power rating, which determines how much power is drawn from the wall compared to the output of the computer. Some older ATX PSUs have efficiency ratings below 70%, while the ATX12V standard requires a minimum rating of 80%.
The aforementioned power supply unit is a power supply unit located inside the desktop computer. Another type is an external power supply.
external power supply
For example, some game consoles and mini PCs have power cords that must be connected between the device and the wall. Here's an example of an Xbox One power supply that does the same thing as a desktop, but is external so it's completely removable and easier to replace than a desktop PSU:
Others are similar, such as some built-in PSU external hard drives, which are needed if the device cannot get enough power from the computer via USB.
An external power supply is beneficial because it makes the device smaller and more attractive. However, these are sometimes attached to power cords, which can make it difficult to place the device against a wall due to their often large size.
An uninterruptible power supply (UPS) is another type of power supply. They are like a backup power supply, providing power when the main PSU is disconnected from the regular power supply. Since power supplies are often victims of power surges and power spikes, since it's where the device receives power, you can plug the device into a UPS (or surge protector).