"Also since the P 15 is being used to re-create an electrical signal why would there be a need to attach it to the wall with a very expensive power cable?"
Definitely any "audio mystery" as to why we PP users get the fancy cable to power it. I have all Nordost from the wall. The MSRP for the PC is nearly half the retail of my PPP!
Reality at least to my ears- aftermarket PC into the PP doesn't "improve" sonics.If it does, it is so subtle if anything.
Even the PS Audio videos don't have a concrete answer as to why you should consider one- you just do it.
Part of the audiophool protocol.