How to Replace a Power Supply in Your PC

Replacing a PSU is straightforward if you follow the right steps

A power supply unit (PSU) replacement takes about 30 minutes to an hour and requires only a screwdriver. You shut down the PC, unplug it, remove the old PSU from the case, disconnect its cables from the motherboard and components, install the new one in the same spot, reconnect the cables, and power on. The hardest part is usually remembering which cables go where — but they are keyed so they only fit one way.

The main reason to replace a PSU is age or failure. A PSU that is five to seven years old, makes a loud noise, or causes random shutdowns is likely failing. Before you buy a replacement, check your current PSU's wattage — it is printed on the label on the back of the unit — and buy one with the same or higher wattage. A higher wattage PSU is fine; a lower one will not work.

Key Takeaways

Turn off the PC completely, unplug the power cable from the wall, and wait 30 seconds before opening the case.
The PSU is a metal box usually in the bottom rear corner of the case; it is held in by four screws on the outside of the case.
Disconnect all cables from the motherboard, graphics card, and storage drives before removing the old PSU.
Install the new PSU in the same position, reconnect cables in the same order, and test the PC before closing the case.
If you are unsure about a cable connection, check your motherboard manual or take a photo of the old setup before disconnecting anything.

Gather the right tools and a replacement PSU

You need a Phillips head screwdriver and a new PSU. That is it. A flashlight or phone light is useful if your case is dark inside. An anti-static wrist strap is optional but recommended if you live in a very dry climate; it prevents static electricity from damaging components.

Before you buy the new PSU, check the wattage of your current one. Open the case, look at the back of the PSU, and read the label. It will say something like "500W" or "750W". Write this number down. When you buy a replacement, match the wattage or go higher — never lower. If you are unsure what wattage you need, a 650W PSU works for most gaming and office PCs; a 750W or 850W is safer for high-end graphics cards.

Power down and open the case safely

Shut down Windows or your operating system normally. Do not force shut down. Once the PC is off, unplug the power cable from the wall outlet. Wait 30 seconds. This drains any remaining power from the PSU and makes it safe to touch.

Open the case by removing the side panel. Most cases have two thumbscrews or regular screws on the rear edge. Remove them and slide the panel off. Set the panel aside where it will not fall. You should now see the inside of the case. The PSU is usually a large metal box in the bottom rear corner, with a fan facing downward or toward the case wall.

Disconnect all cables from the old PSU

Before you remove the PSU, disconnect every cable plugged into it. There are usually four types: the 24-pin cable to the motherboard, the 8-pin or 4-pin cable to the CPU, the 6-pin or 8-pin cables to the graphics card (if you have one), and the SATA or Molex cables to storage drives and fans.

Take a photo of the cable connections with your phone before you unplug anything. This photo will help you reconnect the new PSU correctly. Gently pull each cable straight out of its socket. Do not yank or twist. If a cable is stuck, wiggle it gently side to side while pulling. Some cables have a small clip or latch on the connector; press it while pulling to release the cable.

Once all cables are disconnected, the PSU is ready to come out. You may see cables bundled with zip ties or velcro straps; you do not need to cut or remove these yet — they will come out with the PSU.

Remove the old PSU and install the new one

The PSU is held in by four screws on the outside rear of the case. These screws go through the case wall and into the PSU frame. Using your screwdriver, remove all four screws. Keep them in a safe place — you will use them again. Gently pull the PSU toward you and out of the case. It is heavier than it looks, so use both hands.

Place the new PSU into the same spot, with the fan facing the same direction as the old one. Usually the fan faces downward or toward the rear. Align the four screw holes on the PSU with the holes in the case. Insert the four screws and tighten them by hand first, then use the screwdriver to snug them down. Do not over-tighten; they should be firm but not stripped.

Reconnect cables in the correct order

Use your photo to guide you. Start with the 24-pin motherboard cable. It is the largest connector and only fits one way. Push it straight into the socket on the motherboard until you hear or feel a click. Next, connect the 8-pin or 4-pin CPU cable above the CPU socket. Then connect any 6-pin or 8-pin cables to the graphics card if you have one.

Finally, connect the SATA or Molex cables to your storage drives, SSDs, and case fans. These connectors are keyed, so they will only fit the right way. If a connector does not slide in easily, do not force it — flip it around and try again. Once all cables are connected, double-check that each one is fully seated by gently tugging on it. It should not move.

Test the PC before closing the case

Plug the power cable back into the wall outlet. Flip the power switch on the back of the PSU to the on position. Press the power button on the front of the case. The PC should start normally. Listen for the fans to spin up and look for lights on the motherboard and graphics card. If the PC starts and runs without shutting down, the installation is successful.

Let the PC run for a few minutes. Check that the CPU fan is spinning, the graphics card fan is spinning (if you have one), and there are no error messages on the screen. If everything looks good, shut down the PC normally, unplug it, and close the case. Screw the side panel back on. You are done.

What to do if the PC does not start

If the PC does not turn on, unplug it when ready and open the case again. Check that the 24-pin motherboard cable and the 8-pin CPU cable are fully seated. Push them in firmly until you hear a click. Also check that the power switch on the back of the PSU is in the on position — this is straightforward to miss. Plug the PC back in and try again.

If the PC still does not start, check that the cables are in the right sockets. The 24-pin cable goes to the motherboard, the 8-pin goes to the CPU, and the 6-pin or 8-pin goes to the graphics card. If you are unsure, consult your motherboard manual or look up your motherboard model online. Once you have confirmed the cables are correct, try powering on again.

Frequently Asked Questions

Do I need to turn off the PC before replacing the PSU?

Yes. Always shut down the operating system, unplug the power cable from the wall, and wait 30 seconds before opening the case. This is the only safe way to work on the PSU.

Can I use a PSU with higher wattage than my old one?

Yes. A higher wattage PSU is fine and will not damage your PC. It will straightforward provide more power than you need. Never use a PSU with lower wattage than your current one.

What if I forget which cable goes where?

Take a photo of the old setup before you disconnect anything. The connectors are also keyed, so they only fit one way — if a cable does not slide in easily, it is going in the wrong socket. Check your motherboard manual if you are still unsure.

How long does a PSU usually last?

Most PSUs last five to seven years with normal use. If your PSU is making noise, causing random shutdowns, or is older than seven years, it is time to replace it.

Do I need an anti-static wrist strap?

It is optional but recommended if you live in a very dry climate. If you do not have one, touch a metal part of the case before touching components inside to discharge static electricity.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.