Calculate amps on 12v rail in psu

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nimesha95

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Jan 14, 2015
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Hey, i have 500w genric psu and it's sticker on the side says that it has 20amps on 12v rail. But allow to P=VI
500/12=41.67A. Can anyone explain this to me? Thanks
 
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Calculagator

Calculagator

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Nov 18, 2014
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The PSU is about 500w max, but with a 20A 12v rail, the 12v can only handle 240w. The rest of the 500w goes to 3v and 5v probably. You may have a second 12v rail, but not likely. This is a way for cheap PSUs to give big numbers without actually having capacity.
 
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Math Geek

Math Geek

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Oct 15, 2014
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the total wattage claimed by the psu is a combination of all the rails. each voltage rail is a part of the total and usually adds up to maybe 110% or so of the the rated power since they know you won't pull full power from each rail at the same time. a system just won't do it unless you do it on purpose for testing or something. (3.3v x 32a) + (5v * 32a) + (42v * 12a) = 770 watts total power this psu claims or 154% of it's rated wattage. this is a common ploy with really bad power supplies. they use a lot of 3.3 and 5v amps to make the total power seem higher. then the rails don't even provide the total is says on top of that. i am with sr-71 and the thought you would be lucky to get 30-35 12v amps from it.

really, i would be replacing that psu before the new gpu just to be done with it and forget it ever happened :)

 
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