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I'm buying a new power supply for my computer. I'm considering two models, one is 650W and the other 750W. The 750W one is cheaper than 650W, but my computer doesn't need that much power. I never play any graphic-intensive games. My current 350W PSU is barely doing the job well.

So which one should I buy? If a buy the 750W, will it consume more power in the long run?

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For a different perspective from the accepted answer: superuser.com/questions/446419/… If you install a PSU with too much power (i.e. unneeded) capacity, it will likely consume more power at idle than necessary. How do you know that your "current 350W PSU is barely doing the job well"? –  sawdust Nov 10 '12 at 20:59
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up vote 3 down vote accepted

The rating of the power supply is it's peak rating. That is the maximum power it can deliver.

If you only draw 500W of power (say) then the running costs of the 750W and 650W PSU will be the same - assuming they have roughly the same efficiency rating.

There are many other, possibly more important, factors than cost:

  1. Quality. This is a good guide to the efficiency and life-span of the PSU.
  2. Noise (thanks Richard). You are going to be sitting next to this device for long periods and a noisy fan is going to get annoying (at best) and really uncomfortable (at worst), so look for a quiet one.
  3. Cable management. A more expensive PSU might have more, and more varied internal power connectors so you can connect up all your internal peripherals without extra splitters/converters. Though this is also often a function of the output. A higher rated PSU is going to have more connectors than a lower rated one.

Therefore I'd consider buying the cheapest one that delivers more power than you need, but meets the other criteria outlined above. Having a good margin is useful as you don't have to worry if you add more hard-drives or a more powerful graphics card in the future.

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Hmm I agree with the margin, but i would suggest thinking about efficiency. The cost for drawing 500Watts from those two PSUs is only the same if they have the very same efficiency at the load percentage you are drawing (most likely they won't). Personally i would recommend against buying the cheapest one you can find, you might not need the "diamond 99++++++++" version of course. :-) –  TheUser1024 Nov 10 '12 at 10:53
@TheUser1024 - I assumed the efficiencies were broadly similar –  ChrisF Nov 10 '12 at 10:54
there can be vast differences, check this out (might be a multi hour read, since it is a collection of articles on PSUs): tomshardware.com/reviews/Components,1/Power-Supplies,6 –  TheUser1024 Nov 10 '12 at 10:56
You might also want to consider which one is the quietest. I've got a more expensive 650W PSU than my friends 750W but his makes one hell of a noise even when idle. –  Richard Nov 10 '12 at 10:56
@Richard - another good point - I've been caught out with this myself –  ChrisF Nov 10 '12 at 10:57
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