I've mounted mine facing up (so that the lettering on the side is correct orientation) so that the fan is pointing into the case, but my case has a filtered air intake underneath so I'm wondering if the PSU fan should be facing that?
In an ideal world, your PSU would be taking in 'cool' air from outside rather than warm case air. That said, you may want to use the PSU as extra heat exhaust if you're short on fans. In other news, having the lettering upside down may cause upset/or not...
The PSU is in it's own chamber (case is a Phanteks P600S) so it won't be very effective as a heat exhaust and I'm not bothered about upside down lettering
It looks like the PSU chamber doesn't have much in the way of airflow from the top, so the PSU may not be colled as well as it could be with the fan facing down to the filtered intake in the base.
I'm planning to add another 140mm fan (there are already two at the top of the front of the case) at the bottom of the front of the case for airflow into the PSU chamber because there'll also be a couple of HDDs stacked in there in front of the PSU.
The fans on all the RM series are intakes, they draw air into the PSU. Ideally it should be facing towards the case's intake vent for the PSU so it draws air from outside of the case, then vents it out the back of the PSU outside the case. So on a P600s that would be fan facing downwards towards the floor vent.
