Will a 850W PSU draw 850W from the wall plug?

[barath56]

Question on PSU.
Let's say I buy a 850W PSU (EVGA G2) but my system only use 400W, will my PSU draw 850W from the wall or 400W?

In essence is there anything wrong with getting a higher wattage PSU for low wattage system other than higher price?

I am asking this because I hate to waste energy.

 

[digitaldoc]

The 850W PSU will max out at 850, but if the system needs less, it will provide what is needed.

You do not want a system where the PSU is always running at the max as it will reduce the longevity of the PSU.

 

[bignastyid]

If the system is using 400w the PSU will draw ~445w from the wall depending on the exact efficiency its running at and that psu should be around 90% efficient at that load.

 

[Mr5oh]

I assume you are using an AMD CPU / GPU with a 400 watt draw estimate ?

The PSU will only draw what it needs from the wall, so when your PC is drawing 75-100 watts the PSU is only drawing 85-110 watts from the wall.

Larger to a point is less efficient as PSU are usually most efficient somewhere around 50% load, but the difference on a quality power supply really doesn't matter.