There’s a number of issues here. The results may be different for standard full-wave rectifiers vs. switching supplies, for instance, but in both cases, more storage is almost always a win, the question is “how much more matters”.
For standard rectifier supplies, you can get very annoying 120 cycle-shaped limiting with a weak power supply.
For switchers, the same problem can occur, but not at the “power supply output” rather at the first stage after line rectification happens, if there isn’t enough capacitance to hold up the regulator control range.
So where the capacitor needs to go, and what size and voltage it requires, can vary.
However, adding on millifarad of the right voltage across each pole of the supply to center should never hurt (for low voltage supplies, that is!).
My thought, though, if you’re going to do this (old analog research hardware designer in me is coming out here) go large. Capacitors are cheap.