Hi naggots,
I'm sure Dusty will answer your questions in depth but as a PLC-1 owner I thought I'd jump in. The only function of the power supply on the PLC-1 is to operate the volume, power the LED's, switch inputs, and supply an auxiliary 12v output (a feature I actually use). Otherwise, the PLC-1 is completely passive. So an upgraded power supply is a waste of money since it has zero effect on the signal. The voltage, of course, is a different issue.
BTW, in my experience (and I've owned a number of very fine preamps) the PLC-1 is the cleanest link between sources and amplifier I've ever had in my system.
CSI