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I am starting on planning out a computer. I want to be able to expand the RAM and video cards without replacing the PSU, and I'm not sure if it's safe to get a PSU that provides 750W for a system that'll only require maybe 500W at first. Thanks, all!

marked as duplicate by sawdust, fixer1234, mdpc, Jakuje, Steven Sep 7 '16 at 13:57

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  • Yes, overkill is a good thing.... – Moab Aug 31 '16 at 1:48
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    It's "safe", but the downsides are (1) cost. You're paying for more power capability that you won't be using. (2) efficiency. When the system is at idle, an over-capable PSU will be operating well outside its optimum power range, and use more electricity than a properly-sized PSU. – sawdust Aug 31 '16 at 2:07
  • @sawdust I'm not an expert in PSU's but a PSU will only draw the amount of current that it needs. A 500w PSU is capable of powering 500w, but does not mean it will pull 500w at all times. – DrZoo Aug 31 '16 at 5:25
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    @DrZoo -- The PSU rating of watts is for the max power it can deliver. The power that the PSU draws from the AC line is a function of its load (i.e. the power it is providing) and the (AC to DC conversion) efficiency. This efficiency varies according to the load. See superuser.com/questions/446419/… – sawdust Aug 31 '16 at 20:42
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Absolutely, yes. The rating of a power supply is the maximum that it can deliver. If its maximum is not required, it will deliver whatever is asked.

It is not a problem with computer power supplies, but some cheap, unregulated supplies (such as battery chargers) may give an increased voltage when not at full power.

  • Thank you! I was worried that getting a PSU with too high of a wattage would blow out components. This is my first build. – Isaac Corbrey Aug 31 '16 at 1:32
  • The wrong voltage can damage components, but a higher power rating will cause no problems: otherwise, you couldn't plug a 0.2A lamp into a 13A socket. – AFH Aug 31 '16 at 1:42

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