JB, be sure to keep track of the distinction between a marketing angle that impresses as 'snake oil', and the entirely separate issue of whether the product itself might be described as such.
In my own system, when I got my Levinson 380S preamp - which is not entirely friendly to aftermarket PC's due to its requirement for a right-angle IEC plug, connected on the unit's underside - I asked some dealers who handled the line whether in their experience the piece responded to upgraded PC's. Several sources opined that the internal power supply was so good that no improvement would be heard, and not to worry about a PC change. I wondered if this was a position taken as much out of convenience as of conviction or experimentation, so I persisted until I got another dealer to admit that, yes, it could make a small but worthwhile improvement, but since telling a customer so just created a dissatisfaction that wasn't easily addressed, the other story prevailed. (In fact, the story I heard from all the others was so consistent that I began to suspect that maybe ML reps had hipped them to it as a method of deflecting a predictable objection.) So I decided to prop up my 380S on top of some temporary improvised supports which would allow a straight-plugged cord room to exit without excessive bending and listen for myself. Sure enough, just as I've found with all my other gear, a better cord did indeed make a difference, though in this case the improvement was definitely toward the lesser end of the scale. I think better-designed power supplies can help avoid excessively bad effects from using stock PC's, but I'm not sure it's possible in electronic gear to design-out upgrade-PC benefits completely.
In my own system, when I got my Levinson 380S preamp - which is not entirely friendly to aftermarket PC's due to its requirement for a right-angle IEC plug, connected on the unit's underside - I asked some dealers who handled the line whether in their experience the piece responded to upgraded PC's. Several sources opined that the internal power supply was so good that no improvement would be heard, and not to worry about a PC change. I wondered if this was a position taken as much out of convenience as of conviction or experimentation, so I persisted until I got another dealer to admit that, yes, it could make a small but worthwhile improvement, but since telling a customer so just created a dissatisfaction that wasn't easily addressed, the other story prevailed. (In fact, the story I heard from all the others was so consistent that I began to suspect that maybe ML reps had hipped them to it as a method of deflecting a predictable objection.) So I decided to prop up my 380S on top of some temporary improvised supports which would allow a straight-plugged cord room to exit without excessive bending and listen for myself. Sure enough, just as I've found with all my other gear, a better cord did indeed make a difference, though in this case the improvement was definitely toward the lesser end of the scale. I think better-designed power supplies can help avoid excessively bad effects from using stock PC's, but I'm not sure it's possible in electronic gear to design-out upgrade-PC benefits completely.