Having seen computer cases with power supply units (PSUs) positioned at the top and on the bottom of a computer case (tower), I wonder if there is an optimal place to put the PSU?

It seems that 90% of cases have the PSU at the top, and the reason is partly historical:

The PSU heat exhaust fan also doubled as a heat exhaust fan for the the case as a whole.

On the whole, it works well: most systems are mid – low end, so the components don’t generate much heat, so the PSU is not under much additional heat stress.

However, some high-end systems generate large amounts of heat (due to overclocking and due to high-end video cards that generate a lot of heat).

However, most high-end systems are now built into cases that have multiple fans that usually extract heat before it can get into the PSU.

But if heat is your main problem, then a low-mounted PSU means that it will always draw in cool air.

The other thing to consider is dust.

Having seem many PCs, I know that most PCs have a huge build-up of dust, and most people never bother opening up their PC to clean it.

With dust, a top-mounted PSU is less likely to get a buildup of dust.

Proof of that is when I open most PCs, I usually see a layer of dust at the bottom of the case, but no dust at the top… obviously!

So, when mounting a PSU at the bottom of a case, its important to make sure its unlikely to suck up dust (either by using a filter… which needs regular cleaning, or by regularly “dusting” inside your case.

The only real advantage (that I can see) of having a bottom-mounted PSU, is that the tower is less top-heavy and thus less likeley to fall over if bumped.

So, it seems that in most cases, a top-mounted PSU is best, while a bottom-mounted PSU might be better for a high-end system, but only if you are prepared to clean it every few months.