I've seen a video with Paul from PS Audio where he mentions that the need for fancy power cords with their power regenerators is theoretically unnecessary even though they use very fancy ones. If they do what they are advertised to do then they should produce essentially perfect power and require nothing in front of them.
In my very limited experience with cables, they don't always make an audible difference which may be a limitation with my system. In my case I heard a very clear difference with a different PC on my Pathos Classic One MkIII, but cannot really say that I've heard any difference with different PCs on my DAC (two different ones).
From a purely theoretical perspective I think it makes the most sense to use a good PC on the source where the signal is the smallest and any noise or distortion will be amplified at each successive step (i.e. preamp and power amp).
Some PCs are specifically designed with source components or amplifiers in mind.