So it says...

[ImMrHappa]

This might be a stupid question but i want to make this clear....

 

If the box says that its a 750w psu. its not gonna take that much out of the wall if u have a 400w pc?

[Rashy]

This might be a stupid question but i want to make this clear....

 

If the box says that its a 750w psu. its not gonna take that much out of the wall if u have a 400w pc?

Afaik, no. i dont think so

[zlolslavez]

it may be slightly inefficient but no

[WinNut]

no.

[wyattzx]

The wattage rating of a PSU is its max load. The efficiency rating of the PSU determines, at load percentages, how efficient it can be. For instance: At max load, the PSU should be able to use at least 80% of its 750W rating, for at least a Bronze rating. However, this does not mean it will always draw that much. With the new, power efficient Maxwell architecture on the 900 cards from NVIDIA, high-end builds can draw as little at 350w at max load. 

[quan289]

If the PSU is rated for 750w, it should be able to output the entirety of that 750w rating regardless if it is Bronze, Silver, or Titanium efficient. The difference is the amount of electricity is drawn from the wall and the amount of that energy being wasted during the AC-DC conversion.

 

If a 750w is rated for Bronze, it will draw ~926wAC from the wall if you run the PSU at 100% load @ 115v (176w is wasted as heat). While a Platinum efficiency unit will draw ~843wAC from the wall and wasting 93w as heat.

 

Now if your 750w PSU is outputting 400wDC, efficiency is about 92% on a Platinum unit, as it is near 50% load. That's ~435wAC from the wall