After 30+ years of listening I now feel that the size of a preamp power supply has no more to do with the sound of the music than the size of the woofer in a speaker.
This might be music to your ears but it is probably even more music to a manufacturer's ears.
Are you really suggesting (as a generalization) that a manufacturer can now use a small cheaper power supply and a small cheaper woofer with small cheaper motor and small cheaper voice coil (often no bigger than a tweeter): And in general it sounds better or just as good (in general no benefit from using better parts)?
I agree there is such as thing as diminishing returns and many reasonably sized but well designed power supplies are adequate for the job but please....this is audiophile heresey! LOL - Just Kidding ;-)