How to Detemine What Size Power Supply a Computer Needs

Written by aaron wardell
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When building a computer system, the power supply unit (or PSU) is one of the most often overlooked components. A poor-quality or underpowered PSU can cause failed boot-ups, unexpected crashes and compatibility issues, just to name a few potential problems. In this article you will learn what makes a good PSU and how much power you will need to keep your computer running stable and happy.

Skill level:


    Choose Your PSU

  1. 1

    Invest in quality. Most computers come factory equipped with cheap power supplies that are adequate for most home computing needs. However, if you're replacing a faulty PSU or building a new computer, invest in a quality brand with a good reputation. They may cost more, but they will save you potential headaches down the road. Antec, Corsair, Seasonic, Enermax, Thermaltake and Ultra all make quality PSUs.

  2. 2

    Determine your computer's energy needs. For a modern computer with no power-hungry extras and peripherals, a quality 350W to 500W PSU is usually adequate. Multiple hard drives and CD/DVD drives, a high-end graphics card or dual processors would bump your minimum requirement up to 500W or higher.

  3. 3

    Examine the PSUs +12V specification. The +12V rail powers critical components in your system: the drives, processor and graphics card. 30A is a good number to shoot for if you have a modern graphics card installed. If you have multiple graphics cards or other power-hungry components, you may want to consider 36A.

Tips and warnings

  • Total wattage can be deceiving. For example, a cheap 600W PSU may only be able to supply 18A on the +12V rail, while an expensive 400W PSU will supply 30A. Always check the specifications before buying.
  • If you see multiple +12V rails in the technical specs, simply add the numbers.
  • If you are a gamer with the latest graphics card installed, it pays to buy more power than you think you need. The last thing you want is your computer to crash mid-game because your top-of-the-line graphics card decided to consume 200W.

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