IME they’re additive. Add a better PC, you can get better sound. Add a better outlet, you can get better sound. Add both and you get even better sound. I’ve said it over and over, but in this hobby EVERYTHING MATTERS and makes a difference. And a big +1 for dedicated lines.
Power Cables and Wall Sockets
Without knowing for certain, it seems to me that power cables can only be as good as the in-home wiring coming to the wall socket. Is it possible that those who use expensive cables have improved the wiring to the socket? Or is the power from most wall sockets normally excellent, but is limited by conventional power cables?