So my corsair TX 850 V2 was failing on boot consistently and had to be reset eachtime before use and it would work fine...
In annoyance today I decided to RMA it and got out the back up PSU (Antec HCG 750W). In the process of swapping the PSUs I broke my glasses and in my blind rage I installed the antec upside down. The fan is drawing it's air from inside the case...is this a big deal? I will probably switch back to the corsair in a few weeks...Additionally, I have it in a Corsair Carbide 500r and it has the giant fan feeding air straight into the case and it is right next to the intake fan.
My Antec 900's do not have a vent in the bottom of the case and I didn't bother cutting one, so my PSU's are mounted with the fans up. Two of my three desktops run 24/7 and even when I was load testing, PSU exhaust air was never more than 5 C above ambient and usually 2 - 3 C.
A psu will operate fine right side up, upside down, or even sideways. No problem there.
The job of the psu fan is to cool the psu, and it will spin up only as much as it needs to in order to do it's job.
For an efficient psu of sufficient capacity, it might not even spin at all. So don't count on a psu to help with case cooling.