How to Replace a Power Supply (and buy a good one)

Once upon a time there lived a PC who killed video cards. He was a nice, quiet PC, middle aged and had always performed his duties well. At some point he changed though. He went through several video cards without regard to brand or price and eventually a lengthy investigation uncovered the defect in him responsible. It was his power supply.

I’ve built a dozen computers over the years and up until then I’d never given much thought to the hunk of grey metal sitting anonymously in the various cases I used. In the case of my murderous friend, the trouble did not register with me until I began tracking down possible causes and realized I had moved the motherboard into a new case. Ruling out the possibility my motherboard just didn’t like its new home the only variable left was the included power supply. For the first time in my PC building career I found myself purchasing one as a separate component.

As the cost of energy rises and the debates over global warming rage the potential cost of running one or several computers has become something to consider. I’ve already taken steps to reduce my monthly energy bill outside the home office and recently began to research the possible savings in making changes to my home network.

Things such as turning on hibernation, setting drives to sleep and only leaving computers powered on I need have made a noticeable difference. While pricing components for a future project involving replacing some of my older hardware with more efficient components I was surprised to find that power supplies have evolved. There are “high efficiency” models, “fan-less / silent” models and given the need for cleaner, tighter power among the components available today, the anonymous power supply has become as well-designed as the rest of the computer.

Whether replacing a power supply out of necessity due to failure or an upgrade in components requiring a different design or a desire for reduced noise and power consumption, the process is no longer quite a simple as it once was. Power supplies are now rated for specific processor brand / type and the motherboards connections. The ATX 1.3 standard is being replaced by ATX 12V 2.0 which features a 24 pin mobo connector in place of the former 20 pin and specialized connections for SATA, PCI-express and an optional 4-pin molex for drives.

The best point of reference is your motherboards manual or on-line documentation and if you find yourself replacing failed ATX 1.3 supply, you may want to consider purchasing one of the newer standard ones along with an adaptor cable in order to save money on future upgrades. Toms Hardware has a very well-written stress test review of quite a few power supplies, including a couple of high-efficiency models and wattage ratings from low to outrageously high. Noise and efficiency ratings are also given in the review. These are the variables you’ll want to take into account in order to get a power supply which meets your power / noise preferences and the requirements of your motherboard and components.

Wattage should be calculated to be what your components need plus a little headroom for future upgrades. (Your existing unit should have this printed on the back label and upgraded components also provide power requirements in the documentation or on the box). If your computer only requires 300 watts putting a 1000 watt supply in is a waste of money and electricity. If you are working with a manufactured PC from Dell, Compaq / HP and so on you should either compare the existing unit to available replacements or purchase a replacement from the vendor as these sometimes have specialized connections outside the ATX standard.

Things to consider when purchasing a new power supply:

  • Motherboard connection type
  • Specialized units, (Dell, Compaq / HP and others)
  • Warranty (You may void it by replacing a factory supply on your own)
  • Wattage needed (look at the back of your existing supply)
  • Noise level
  • Desired power efficiency

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Comments (9)

  • Philip says:

    In the hardware failures I’ve seen, the most common part has been the power supply. Then again, most of our computers are Dell. I shouldn’t be complaining, as they are so easy to change. A quick check with a PSU tester makes verification easy.

  • Bryce W says:

    Same here, especially lately. In the suburbs neighboring my office they are building a major highway and the construction is causing frequent power surges to nearby houses. It has tripled the amount of jobs for power supply replacements.

  • Andrew B says:

    The good place to figure the necessary PSU Wattage and Amperage is

    I use it all the time and results are pretty accurate.

  • chebangs says:

    I had an experienced on power supply failure before and I find really hard pointing it. The system runs normal but when using the cd/dvd rom drives it will crush and sometimes it will restart or shut down. I replace new cd/dvd rom and still has the problem. It really takes time to pin point the problem.

  • tyree says:

    great reviews

  • Rick Work says:

    Wow! Thank you! I always wanted to write in my site something like that. Can I take part of your post to my blog?

  • Mike says:

    It’s also a good idea to carry a Volt Meter to check Amps and more then the PSU Tester can.

  • Scott Cairns says:

    Just keep in mind that a PSU tester does not test the power supply under load, and thus may not be enough to diagnose a failing unit. I have come across a few units in my day that test fine, but the computer will still not post until I put in a new PSU.

  • Saty says:

    So, what is a good way to pin point a faulty power supply unit? Cany anyone make a good suggestion?

    The point that Scott Cairns has made is a very good point.