DIY Technology Explained

Can I Reuse My Old PC’s Power Supply in a New Computer?

Christian Cawley Updated 03-03-2020

One of the best ways to reduce the cost of upgrading your PC is to re-use some old components. You can retain some parts, like the sound card, DVD drive, and particularly the power supply unit (PSU).

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In the case of the PSU, this could save you up to $150. While the graphics card, CPU, motherboard, and RAM might need upgrading, the PSU doesn’t.

But is your old PSU truly reusable? Can you use an old power supply for a new computer? Let’s find out if will be reliable and have the power required.

Finding and Removing Your PC’s Power Supply Unit

Desktop PCs, whether tower (vertical) or horizontal, will have the power supply unit on the reverse. Alongside all other cables for sound and USB devices, you’ll find the power cable connected. This will be accompanied by a standard on-off rocker switch and an outlet fan for cooling.

The old PSU will be found on the back of the PC

Now you know where the PSU is on the back of your PC. But what about on the inside?

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Before proceeding, ensure the PC is shutdown and the PSU disconnected from the mains. You should also take anti-static precautions What Is Static Electricity? And How to Get Rid of It Concerned about static electricity? If you're building a PC, you should be. Learn how to get rid of static electricity today. Read More to maintain the integrity of your hardware.

If you remove the case, you should see the PSU, or at least work out its position. But it might be difficult to physically reach. This will typically be down to the next of wires, but it might also be due to the position of the DVD drive, or even the CPU fan and RAM.

To remove the PSU, safely remove the power cables to the motherboard, CPU, disk drives, and other components. Bundle these over the side of the case, briefly securing with a cable tie.

Next, remove the PSU’s securing screws on the back of the case. Save these for later, then pull the PSU out of the PC case.

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You should always remove the PSU from the case first when dismantling a PC.

Understanding Your Power Supply

While the specs of your computer system can be analyzed with benchmarking tools The 10 Best Free Benchmark Programs for Windows Use these fantastic and free benchmark software for Windows to troubleshoot your system and keep it updated. Read More  the PSU is different. To learn more about it, you’ll need to look at the device.

You should have noticed that the PSU features a label listing its maximum output and other information. While the labels differ depending on model and manufacturer, there should be a section describing maximum load or output.

All PSUs feature a label of specifications

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That is the total amount of power that the supply can handle overall. You can use that figure and compare it to what’s recommended for the new hardware you’d like to purchase.

Most PSUs also feature a section describing output for each type of voltage. That’s the list +5V, +3.3V, +12V and etc. Each value is shown alongside an amp rating. Pay close attention to the 12V value (aka rail). The graphics card, which is often among the most power-hungry components in a system, draws power from it.

To run a moderately powerful graphics card, look for a PSU with around 30A on the 12V rail.

If the maximum wattage and 12V rail are enough for the components you’re installing you should have no problems.

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Will the Old Power Supply Remain Reliable?

Some manufacturers are reliable and make power supplies that perform up to or even beyond their specifications. Others are more concerned with shifting units. To find out more, find your PSU’s brand (listed on the label) and check its reputation online. No brand? Maybe time to buy a new PSU.

Bad things can happen with poorly manufactured power supplies. A PSU labelled 750-watt might struggle to supply over 500 watts. Some supplies will even smoke and burn when they fail.

While old power supplies might still work, it could be because your old PC hardware didn’t need too much power.

Upgrading the CPU, motherboard, and graphics card could change that.

A supply that fails can, in the worst case, take out other components in your PC or even catch fire. Upgrading to a reliable drive from a company like Antec, Corsair or Cooler Master is often the better choice.

Connect an Old Power Supply to a New Motherboard

After confirming the capability and capacity of your old PSU, make some checks:

  • Dust the PSU down—you might need a vacuum cleaner to draw dust out from the fan.
  • Ensure cables are all in good condition with no splits in the insulation.
  • Confirm the plugs are not cracked or broken.
  • Compare the plugs on the PSU with the motherboard and other new components you’re planning to upgrade.

(As some connectors are omitted on old power supplies, this could prevent using an old PSU in your “new” computer.)

While modern motherboards accept a 24-pin primary power connection, some old PSUs will only have a 20-pin plug available. Fortunately, these are rare—while the 20-pin plug might work, it is best avoided. If there is also a 4-pin (two by two) connector you should be okay. This will probably feature a slot to fix to the 20-pin strip.

Current computers require more power than a 20-pin supply can deliver. Relying on such a PSU is likely to result in power failures, which can cause issues with the operating system. This can also impact the integrity of valuable personal data stored on your hard disk drive (HDD).

Some motherboards require an 8-pin (two rows of four) secondary connection for the CPU. A CPU will often run without with just a 4-pin connection, but it may be unstable in certain situations. A Molex to 8-pin ATX adapter usually resolves any problems that might occur, such as from overclocking.

2 Pack 4-Pin Female to 8-Pin Male ATX 2 Pack 4-Pin Female to 8-Pin Male ATX Buy Now On Amazon $9.59

Connecting Modern PC Components to an Old Power Supply

It isn’t just the motherboard you’ll need to connect to the old PSU. Graphics cards and storage devices need power and there’s a good chance you’ll need some adaptors for compatibility.

Video cards were once content drawing power straight from a motherboard. While most motherboards feature integrated video output, gaming requires discrete graphics cards.

While prices (and power) vary, even inexpensive cards usually need a dedicated 6-pin PCI Express power connection. Some even need two 6-pins or an 8-pin. You’ll often be able to power the card using multiple Molex connections with an adapter.

Cable Matters 2-Pack 8-Pin PCIe to Molex Cable Matters 2-Pack 8-Pin PCIe to Molex Buy Now On Amazon $7.49

Some video cards might come with these adapters in the box. But note that more powerful cards may not work with this solution.

When it comes to HDDs and Solid-State Drives (SSDs), you may find the old PSU lacks SATA power connectors. Again, an adapter can be used, this time a Molex to SATA adapter.

3-Pack 4 Pin Molex to SATA Power Cable 3-Pack 4 Pin Molex to SATA Power Cable Buy Now On Amazon $6.99

What If You Can’t Use Your Old PSU?

Hopefully you’ll find that you can use your old power supply and save yourself a few bucks. Just make sure it’s up to scratch, take some time to clean it, and ensure the cables aren’t worn. Check the voltage rating to ensure it’s suitable for your new PC build.

If not, it’s time to replace your old power supply.

You’ll find the choice of replacement power supply units is considerable. To help, check our guide to buying a new PSU 6 Things to Know When Buying a Power Supply Unit (PSU) Power supply units aren't as glamorous as processors and graphics cards, but they're a critical PC component that you absolutely cannot overlook. Here's what to know when buying one. Read More before you commit to spending.\

Image credit: Wavebreakmedia/Depositphotos

Related topics: Building PCs, Computer Maintenance, Computer Parts, PSU.

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  1. Bogdan Chirita
    January 15, 2013 at 5:50 pm

    We had a batch of computers at work with sources that seemed programed to crash. Within 6 months al were broken.

  2. Eric Wilborn
    December 25, 2012 at 2:59 am

    I've used an old one to revive a friend's computer more than once. Great re-use technique.

  3. Samarth Hegde
    December 23, 2012 at 6:28 am

    IT's always better to confirm the gauge of the wire ... And examine the condition
    before buying it.. :)
    And some wires having sockets has to be examined clearly... Because vendors usually cheat by giving rusted sockets... AND its important the sockets are spaced in proper distances or else has high probabilities of getting shorted.. :)
    Good article liked it. :)

  4. Salman Johnson
    December 20, 2012 at 10:47 pm

    Corsair is the way to go

  5. Phil Botsky
    December 20, 2012 at 7:29 pm

    Informative article. Thanks for it. I always prefer new one in new PC.

  6. Jim Carter
    December 20, 2012 at 6:46 pm

    It won't be a "new" computer any longer if it has used parts.

    This is about as silly as asking: "Can I use my old refrigerator shelves in my new refrigerator?"

    A new PC comes with a new power supply. If you're foolish enough to build your own, then you should be able to afford an extra $49 for a new power supply. If not; wait until you can afford it.

    • Tina Sieber
      December 21, 2012 at 2:34 pm

      What is the problem with re-using parts? I can see how an old power supply may cause a problem, but generally re-using things that are perfectly fine should be systematically encouraged. It should be easy and beneficial for the user. Less money spent, less stuff to worry about, less trash.

      • Jim Carter
        December 21, 2012 at 5:37 pm

        Building your own PC is foolish from cost to warranty to incompatibility issues. Buy a whole, new PC from a trusted, local dealership that uses quality parts. Wipe the drive in the old PC and sell it as a whole, used PC. Less hassle all the way around.

        • Matt Smith
          December 22, 2012 at 12:59 am

          You sound like you run a trusted local dealership. Just saying.

        • Jim Carter
          December 22, 2012 at 1:17 am

          Yes....one who has fielded dozens of calls from individuals who assembled computers that ultimately won't boot an OS.

        • undrline
          November 7, 2016 at 6:33 pm

          I've never had a computer place make good on their warranty. It was always not covered, or your fault.

          I suppose it depends on why someone's building their own PC. If the intent is for it to be modular so when something needs fixing or upgrading, you can simply change out a part rather than the whole thing, then it makes sense. If the intent is to have a custom build, because what you want isn't off-the-shelf, then it also makes sense.

        • Mike Walsh
          March 17, 2020 at 1:28 am

          .....and it sounds like said individuals obviously didn't have a clue what they were doing. Just saying.....

          Anybody with a modicum of skill and an ounce or two of common sense, along with the patience & ability to effectively research everything they intend to do, can assemble a modern computer with very little hassle. The internet is full of sound, practical advice on such matters; it ain't exactly rocket science. Of COURSE a dealer is going to 'pooh-pooh' such a course of action.....it threatens his livelihood, after all. Again, just saying.....

  7. Scott Macmillan
    December 20, 2012 at 5:38 pm

    Thanks for the article.I think I will be buying a new one and upgrading rather than using the old one.

  8. Nicola De Ieso
    December 20, 2012 at 5:26 pm

    I change the older pc's power supplier for security.

  9. jasray
    December 20, 2012 at 5:07 pm

    Yes, most likely. Wouldn't recommend it because an old power supply unit is going to run louder, hotter and with lower power output. Invest in a new one--they are relatively inexpensive.

    • Matt Smith
      December 20, 2012 at 6:57 pm

      I have a four-year old Antec EarthWatts and Corsair 750 Watt that are still going strong and cause no problems. But bother were relatively expensive for their wattage when I bought them. I think they're paying off over time.

  10. AP
    December 20, 2012 at 4:52 pm

    Well I found your article very valuable and advised my friend about this who was being fooled by the vendor . Thanks.