People's Thoughts On: Location and Orientation of PSUs

So this is sort of a question and sort of a discussion. I'm trying to form an opinion myself, but I chose to list this as a discussion since I expect the ultimate verdict to be something along the lines of, "It's up to you and your personal judgment/preference." Everyone will certainly have their own opinions and experiences. But here I go anyway:

What are people's thoughts on the "proper" mount location (top or bottom) for the PSU in a tower case?

And if bottom, should the fan be placed facing up or down?

(I suppose one could technically top-mount a PSU such that the fan faces up and takes in air from above the tower through the top vents (if there are any), but this seems silly and is not common practice as far as I'm aware)

My perspective on/understanding of the matter (thus far) is that whether you opt for a top-mounting case or a bottom-mounting one is not particularly important, as PSU cable length has probably increased somewhat over the last several years to compensate for the introduction of the once-troublesome bottom-mount. This negates one of the more prominent arguments against bottom-mounting that I've read.

The bottom-mount's original purpose, as I understand it, was to isolate the PSU from the rest of the components and to provide the PSU with cooler air than it would receive if it were top-mounted, thus prolonging its lifetime. This, then, would mean that it would make little sense to have a bottom-mounted PSU's fan facing up into the case, as that would disrupt the flow of cooler air up to the CPU and GPU fans. So supposedly a bottom-mounted PSU should always be oriented with the fan downward, drawing cool air in from underneath the case. This would come with a few caveats. 1) The case must have a bottom vent so that "fresh" air can be drawn up into the PSU. 2) That vent should have a dust filter, since a fan so close to the ground is liable to get clogged with dust and dirt very quickly. 3) The case must be elevated off the ground with feet of some kind (for ventilation).

Another argument I've read against bottom-mounted PSUs is that they necessitate another fan in the system—namely, a top rear exhaust fan. This extra fan, of course, makes the machine louder.

But my understanding is that early (top-mounted) PSUs, unlike those of today, did not have temperature detectors and speed variability. They just ran at full speed all the time, and so constantly moved quite a lot of air, rendering any additional top-rear exhaust redundant. Today, though, PSUs cannot serve that function quite so well since they often run at low enough temperatures and slow enough speeds that they don't move much air at all (even when under heavy load, if they're good quality PSUs). So it makes sense to relocate the PSU and add an exhaust fan.

At this point, I'm left to conclude that the ideal set-up (assuming we are working within the limitations of air cooling) is a bottom-mounted PSU that faces fan-down into a filtered vent that is elevated off the ground, where both filter and PSU fan hygiene are maintained. I don't think modern PSUs are cut out for the job of rear exhaust fan, and the old problems with cable-routing are a thing of the past.

Thoughts? Agree? Disagree? Think I'm mistaken about some of my facts, arguments, or lines of reasoning? I'd love to hear :)
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  1. Good job of reasoning. New seeds to think on, when psu got bigger and heavier top mounting psu made pc top heavy and likely to tip over. Psu need incoming air to be cooler as possible to main efficiency.
    with caps in a power supply if there the cheaper 85c ones and in a small case at the top. you could heat the ps where you can shorten the life of the caps. newer better power supply use higher temp 105 or higher caps. having the power supply on the bottom keeps it cooler. it also help in the convection effect in the case. the hottest parts now are the gpu and not the cpu.
    most newer intel cpu with a good heat sink are barely warm at all. also in the 90 with at and then atx mb. some vendor did not use standard mb and power supplys. also a lot of vendor back then put there power plugs anywhere on the mb and most power supply were not moduler as they are now. most good pc vendor now putting there cables connection in places that work right for the builders to keep the cables from looking like rat nests.
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