Power Supply fan direction

[Va1heru]

I always assumed that power supply fans were supposed to blow air out instead of sucking it in. But today I just checked my computer and the direction of the fans and noticed that both of my fans were sucking air into the computer (the power supply fan and the bottom front mounted fan. I had my power supply fan replaced a little while ago and I am wondering if the guy who replaced it put it in backwards or if this is how it is supposed to be.

 

[Jhhnn]

Definitely blowing out. Some older atx psu's had the fan on the bottom blowing in across the processor, but even these generally give better results if the fan is reversed to push air thru the psu to the outside of the case.

 

[SWScorch]

I believe that the original ATX spec had the PSU sucking air in and then letting it waft over the CPU. Later theyr ealized this was not the best solution and reversed it to blow air out. You definitely want the PSU fan to exhaust all that hot air from your case.