How to Install a PSU: An Extremely Easy Guide

Get your PC hooked up and running in no time

Written by Eric McClure

Last Updated: July 28, 2025 Fact Checked

This wikiHow teaches you how to install a power supply for a Windows desktop computer. The power supply is what facilitates the flow of power from an electrical source to the other components of the computer. Keep in mind that if your computer came pre-assembled, you don't need to install the power supply, though you may eventually need to replace it.

Installing a Power Supply: Quick Steps

Ground yourself and open the PC case.
Set the voltage on the power supply to 110V or 115V.
Insert the power supply and screw it into place.
Attach both power cables to the motherboard.
Attach the power supply's smaller cables to other components.

1

Select an appropriate PSU.

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The power supply must be compatible with your PC. The power supply that you buy depends on the computer's motherboard and housing size, meaning that you'll need to research your motherboard model to see which power supplies will fit.^{[1]
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Research source} Also, look up your GPU and CPU voltage requirements and buy a PSU with more total voltage than you need for both components.^{[2]
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- For example, if you need roughly 650 watts for your PC, you likely want at least a 750-watt PSU. You won’t do any damage by buying a PSU with way more wattage, but it’s likely a waste of money.
- Make sure that you buy a power supply that is optimized for your region. Power supplies for European markets use different voltage settings than those used in North American markets, for example.
- You can check a PSU’s compatibility using PC Part Picker’s build tool.

2

Gather your tools.

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Get a screwdriver that matches the screw shape. You'll need at least one screwdriver (typically a Phillips head) to open the CPU housing, which is usually the right-hand side of the CPU box when looking at the back of the box. You may need a different screwdriver for your power supply as well—look at the screws that came with the power supply to determine whether or not this is the case.
- Some cases don’t have screws, but latches. Even if you don't need a screwdriver to remove your case, you'll still need one for the PSU.

3

Ground yourself.

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Grounding yourself will keep you from accidentally damaging anything. This will help prevent you from accidentally damaging the internal components of your computer with static electricity.^{[3]
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Research source} To ground yourself, either touch a piece of bare metal or buy and wear a grounding strap.^{[4]
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- Key tips on remaining grounded as you go:
  - Don’t work in your socks. You’re probably doing this at home, but work barefoot instead of working in your socks.
  - Only put your PC on a wooden or stone surface while you work.
  - Avoid doing this in a carpeted room.
  - Periodically tap on a piece of bare metal to discharge any static.

4

Remove your PC’s side panel.

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Shut the power off, unplug the PC, and open the case. For most cases, you either remove the screws on the back or you simply lift the panel up. You will likely have to remove the top panel first to access your side panel. You should be looking at the computer's internals at this point.
- Every case is different, so if you can’t find a way to get into your PC, look up the case model online and find the manual.

5

Remove the old PSU, if necessary.

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If you’re replacing a PSU, take the old one out. Start by disconnecting every cable that runs from the back of your old PSU to a port on the motherboard. Then, confirm that everything is unplugged from the PSU, including any hard drives or SATA SSDs that may be tucked into a hidden compartment. With everything unplugged, use a screwdriver to remove the fasteners holding the PSU in place and pull it out.^{[5]
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- If it has been a really long time since you installed the PSU or the computer is prebuilt, the PSU may stick a little bit in the case. Don’t worry about damaging anything if you have to jiggle the power supply out a bit.
- Take a photo before disconnecting everything if you’re new to PC building. If the computer was working in the past, taking a photo of where all of the cables run will make replacing the PSU a lot easier.
- Do not reuse your old PSU cables—this will destroy your new PSU. The only cables you should use with your new PSU are the cables that it came with.

6

Set the PC on its side.

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Set the exposed side facing up. Carefully and gently tip the PC over with both hands. Gently lay the case on whatever side is opposite the open panel.
- Avoid the temptation to put a towel or some other fabric material down under the PC to protect it. That can create static electricity as you work.

7

Set the voltage on your new PSU.

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Set the power supply's voltage switch. If there's a voltage switch on the power supply, switch it to the 110V or 115V setting. This will ensure that your power supply provides ample power without damaging the components to which it's connected.
- Not all power supplies have voltage switches, and those that do normally have the switch set to the standard of the region for which they were purchased.
- In the United States, you typically set your voltage to 110.

8

Preinstall the cables (modular PSUs only)

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If your PSU is modular, identify which cables you need and plug them in. Modular PSUs come with a lot of cables and slots. You are not likely to need all of the connections, so figuring this out before your PSU is installed will save a lot of headaches. It’s also much harder to plug in new cables when the PSU is already in the case. Note that you must use the cables that came with your PSU. You cannot reuse old cables.^{[6]
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Research source} In general, here are the connections you likely want/need:
- 24-pin ATX: This powers your motherboard.
- 4x4 or 8x8 CPU: These power your CPU.
- PCIe (6+2 pin, or 12VHPWR): This powers your GPU.
- SATA: These are the most common cables for SATA SSDs, hard drives, and optical drives. If you have an elaborate fan setup, you may need a SATA cable for the controller.
- Molex: You probably won’t need these, but they may be handy for older components, fans, or peripherals (like internal display screens or WiFi cards).

9

Locate the power supply bank in the case.

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Find the power supply's intended location. Power supply units typically sit inside of an enclosure at the bottom of the case, furthest from the front. In rare scenarios, the case manufacturer may put the PSU bank at the top, but that’s the exception, not the norm.
- Refer to your computer's instruction manual for the proper placement of the power supply unit, or look for a rectangular cut-out on the back of the case.

10

Insert your new PSU.

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Slide the PSU into the bank. The power supply should have a distinct “back” with plugs and a fan, as well as a “bottom” with a fan on it. The “back” should face the back of the case, while the “bottom” should point away from the case (either to the bottom or side). If you can see the fan from outside the case, it’s oriented correctly.^{[7]
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- The fan on the PSU will turn on automatically whenever the power supply begins to overheat. If the fan is pointed towards the components, it’ll just pull hot air into the PSU, which won’t help it cool off.

11

Screw the PSU into place.

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With the "back" of the power supply unit pressed against the back of the case, insert the included screws to lock the power supply into place. Do not use any other kind of screw. You must use the screws that came with the PSU.^{[8]
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12

Connect the PSU to the motherboard.

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Attach the power supply to the motherboard. Find the main power cable on the power supply (usually the one with the largest plug) called the 24-pin ATX cable. Refer to your motherboard’s manual to find which specific port it plugs into. In most cases, it plugs into the right side of the motherboard.^{[9]
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- Worried about plugging into the wrong port? Don’t be. Modern motherboards and PSUs are designed kind of like puzzles where the pieces will not fit together if they aren’t meant to connect. If you hear the pins click in place with your cable, you did it right!

13

Connect your PC’s additional components.

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Connect the power supply to the other computer components. Using the additional cables, connect the power supply to the rest of your PC’s parts. If you have other components in your case (e.g., a lighting system), you may need to plug these in as well.^{[10]
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Research source} Generally speaking, you likely want to connect:
- 4x4 or 8x8 CPU: The CPU header at the top of the motherboard.
  - If the CPU cable has both a 4x4 and an 8x8, search your CPU model online to see which one you should use. For modern CPUs, you usually use the 8x8.
- PCIe (6+2 pin, or 12VHPWR): The slot on the GPU.
  - Your PCIe cable likely splits. If you don’t have slots on your GPU for all of the cable’s ports, it means your GPU doesn’t need the entire cable. You can just let the other portion of the cable hang freely or tuck it in somewhere.
- SATA: Any storage drives (except NVMe SSDs, which are installed directly on the motherboard).
  - Many builds will require multiple SATA cables.

14

Plug the PSU’s power in.

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Lastly, grab the power cable and stick it in the back of the PSU. Your PSU came with a large 3-pin cable. That’s the power cord. Stick the female end into the prongs on the back of the PSU, then plug the male end into a wall outlet.^{[11]
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- Flip the switch on the PSU, too. Your PSU has an emergency shut-off toggle, almost always next to the slot for the power cable. Flip it to ensure power actually gets to your PSU.

15

Test your PC before closing the case.

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Turn on your computer and close the case up. If everything is connected and powered properly, the fan on the power supply should turn on, and your computer will boot like usual. If you hear a beep and nothing happens, then something inside is not connected correctly, or the power supply is not providing enough power to your components.^{[12]
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- Don’t jump right to the PSU as the primary problem if your PC doesn’t post. If the fan on the PSU turns on and everything in the computer lights up, the problem is more likely your motherboard.

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Question

What could it mean if my computer starts but is unresponsive?

Community Answer

Something on the inside is not plugged in, like the 12v 4/8 pin.

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How do I test to see if a power supply is functioning?

Community Answer

You can either buy a PSU tester or take a paper clip and fold it into a U-shape. On the 20/24 pin power cable, put one end of the paper clip in the slot that the green wire runs into. Then put the other end in the slot that any black wire runs in. Plug the PSU into a wall plug, and flip the switch on.

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Should the fan face into the case or out of the case?

Community Answer

It depends on whether you want the power supply to affect the air pressure of the machine. If you want to have a more negative air pressure, aim the fan into the case. However, this could lead to a slight temp increase for the PSU, which could, in turn, mean louder operation.

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Tips

You may have extra cables once you've finished connecting the power supply to your computer's components.^{[13]
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Warnings

Remember that all power supplies contain various capacitors inside them that retain power even after it has been turned off. Never open up or insert any metal objects into the vents of it, as you can risk electrical shock.

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Always use the new cables that come with the new PSU. Never try to reuse the old cables from the old PSU, as that can fry your motherboard.

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The power supply's connections to the internal components must be snug, but not forced. Don’t shove anything where it doesn’t belong!^{[14]
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