What does a 650w PSU draw when idle?

[Jayce]

Just a typical power question:

If your computer has a 650w PSU, is it drawing 650w constantly from the wall outlet and just supplies wattage from that 650 pool to the components when needed?

OR

If your computer has a 650w PSU, is it only drawing from the wall outlet what the current components require? Meaning if your current components require 400w, is it drawing 400w with the PSU having a capability of 650w? Or is it constant @ 650w?

 

[Lexluethar]

I believe it always draws the 650watts (or near that). Reason being is you can test any one of the connectors on a PSU when the PSU is turned on and you can measure the voltage being used (done all the time when testing the 12 volt connector when a PSU is the suspect for a computer not working).

That is my thought at least, i don't know for sure. But it seems to me when the PSU is on, it is drawing how much power it is rated for. Again i just come to that conclusion because you can test any of the connectors and you get a reading.

 

[kmote]

The second one. Case in point a friend of mine bought a 1000W corsair PSU for his dual CPU machine and when he measured what it was drawing from the wall? 250W.
Lex what you were measuring there is the volts - these are supposed to be as rated at all times the difference comes from the amps that are drawn which are variable.

 

[Lexluethar]

Well there you go. Thanks for the info!

 

[TheMajor]

It will draw the amount that is needed by your computer, plus its inefficiency.

If your PSU is 85% efficient at 100W, then it will draw 115W from your socket. Sometimes you can find the efficiency specifications online.