Relationship between GPU recommended wattage and the PSU

[Charlie98]

I'm confused.

EVGA specs a 600W minimum PSU for that card, I think the PSU you picked is perfect.

I made that recommendation in another thread... the OP had spec'ed a 650w PSU to go with his new GPU that had a recommended minimum PSU rating of 600 watts.

Then lehtv burst my bubble...

although the 550w version would be fine too

...and I've seen that recommendation (a lower watt PSU than recommended for the GPU) a few time before.

Evga has recommended a minimum of a 550w PSU for my 560ti 448 GPU. OK, but when I test it using a Kill-o-Watt (at the wall, for the entire PC) throwing everything I can at it, I'm lucky to draw 400 watts... I think the highest I've had it was 452w, with an OC'd GPU.

Why do the manufacturers recommend such a high wattage PSU? Now, I know it isn't necessarily just the watts... there is amp draw as well. I understand they want to make sure the PSU can handle the entire system, not just the GPU, but... I'm not running 20 HDD's.

What gives...?

 

[Torn Mind]

Making sure they aren't liable for users using mislabeled PSUs and then killing their own system afterwards.

Diablotek, Logisys, etc make units sold for $20 for an alleged 480 W unit that can't even pull 300 watts. Often, the Schottky rectifiers or MOSFET on the 12v rail have too many amps going through them. It could be the bridge rectifier is actually 4 diodes that can't handle nearly enough amps to meet the rated paper specs. Or it could be some other deficiency. These "lemon" units are going to be purchased, and if one of them blows, the GPU manufacturer could be at risk for being blamed because their product "pulled too much power" and could wreak units since many end users don't know any better. The bad press could lower sales volume, and they suffer. These overstated units often pull only half their rated wattage, so the GPU manfacturers take that into account when making their recommendation.

 

[Charlie98]

Jeepers...

 

[Puffnstuff]

Having headroom protects you and them.

 

[lakedude]

A PS is generally most efficient at mid-range. If someone needed 250 watts all the time a 500 watt PS would be more efficient than say a 300 watt PS. The 300 might work (it is best not to push these things) but the 500 would be better.

 

[thedosbox]

I think we had this discussion recently:

http://forums.anandtech.com/showthread.php?t=2366190

 

[Charlie98]

I think we had this discussion recently:

http://forums.anandtech.com/showthread.php?t=2366190

By golly, your right... I never even saw that thread.

 

[ghost03]

Just because a given PSU is rated for, e.g., 300 watts doesn't mean that power is distributed between the 3v 5v and 12v rails in a way to support a system that draws, e.g., 200 watts. Moreover, even if it is, while that system might commonly sustain 200 watts, it could potentially have peaks in excess of 300.

Its good to have a PSU capable of more output than the system draws just like its good to have a bridge that can hold more weight than is on it.