How much is too much?

Right, first time building my own comp and I worked out (using the handy calculator link on this forum) that if I get a crossfire system setup in the future I'll need ~500W.

I understand that using less than total capacity on a PSU is good. So, if that's true and I'm not gonna draw loads of power or run crazy hot, then how much extra capacity is too much? I was thinking of getting a 635W...
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  1. It's not the total wattage on the PSU that's important, its how much is on the combined 12V rails since thats where most of the power is pulled from. There are alot of high wattage PSUs that can be hammered by lower wattage ones. What PSU specifically were you looking at and what system to run?
  2. Well, I'm looking at several models all between 550 and 700W. The 12V rails on all them are like: 12V1@19A or 20A, 12V2@19A or 20A, and -12V@0.5A or 1A.

    Specifically, I was leaning toward the COOLMAX CXI-600B ATX12V 600W Power Supply 115/230 V - Retail (

    I'd be running a Core 2 Duo E6750, 2GB DDR2, (maybe eventually two, now one) Radeon X1950 pro cards, a motherboard to match, 7200rpm SATA Drive...
  3. Here is a great PSU that I'm glad to own. Theres one for SLI or CrossFire.
  4. Thanks... may be a bit too expensive for my taste though. So if I ran a 750W PSU on my computer, which probably needs only 500W, I'd be fine? Does this cause some sort of inefficiency or heat problem?
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