As in an audio installation, that would be pointless.
Not to my knowledge has anybody done it on these forums.
You could be the first.
A computer drains a lot of power, so a capacitor would drain very quickly. And also since this is not reproducing audio signals or anything else, mild fluctuations in voltage, are fine. It is normal, and that's what a ATX power supply is meant for. To filter that out. And guess how it is done? Huge coils and capacitors.
So another capacitor would be a double redundancy.