Yes my experience was similar. Did you use special wires in wall, or just stuck with stock construction stuff?
The surprise, as I was telling another loose-walleted friend around here, was that even with this I still preferred my ps audio p10 plugged into the dedicated wall socket over just direct to the dedicated wall socket.
In second place was my p5, yes sadly I can hear an improvement for the p10 over the p5.
Last of all was direct to the dedicated wall socket.
You can buy audiophile grade wiring from Cardas and JPS Labs but I've never read any comparisons from anyone who's actually used this expensive wire. I happened to find an electrician who is also an audiophile and he was very helpful in his guidance. He was the one that directed me to Vince Galbo's article.
I have 4 dedicated lines in my home (2 for my HT which were installed years ago and 2 for my 2-channel/headphone setup that were installed earlier this year). The problem with multiple dedicated lines for any setup is the likelihood of ground loops. This was the case with my 2-channel/headphone setup. My subwoofer hum disappeared completely when I put everything onto one circuit and so YMMV. A single 20A circuit can supply 2400 watts (120V) or 1200 watts (240V), which is plenty for most people's needs.
In my HT, it was wired with Romex 10AWG/2 but with my dedicated lines for my 2-channel/headphone setup, I went with 10AWG/3 at the recommendation of my electrician which wasn't any more expensive. Your electrician may question the use of this wire which contains 2 hot (black + red), 1 neutral (white) and 1 ground (green) wire but the reason to use 10/3 wire is that this cable has a natural twist which reduces interference transmission. Furthermore, my electrician used one of the hot wires and combined it with the ground wire so that the ground wire was comprised of 2 wires to further reduce resistance of the ground wire. In his theoretical view, to have as big a drain as possible was ideal.
As highlighted in Vince Galbo's article, the main goal of a dedicated circuit is not so much to have a clean signal but to reduce resistance, not just for power hungry amps but also for digital gear like DACs and music servers. While such devices don't require large peak amounts of current, they often require very rapid transient current delivery which can easily get choked by 12g or smaller wire. This is another reason to have a single uninterrupted large conduit connecting your receptable to your circuit breaker. If there are side branches feeding other receptacles, it will have an impact on the resistance of your line.
Clean power is a secondary benefit. While it will have no impact if your utility's power is dirty, it will guard against noise from other circuits in your home (refrigerator, microwave, HVAC, etc) which often is the main source of dirty power in most homes. If you are noticing benefit from an AC regenerator despite having a dedicated circuit, it usually means your utility company's power output is dirty. The problem with AC regenerators or any device that is transformer-based is there is often a trade off -- you get a lower noise floor but you give up dynamics, even with low power DACs. This is one reason why you might notice the P10 sounds better than the P5 even though the P5 should in theory provide plenty of power. The question then becomes whether a P20 (assuming it existed) would sound even better than the P10. Sometimes, you have no choice but to use an AC regenerator because the positives outweigh the negatives. I brought in an AC regenerator into my home once and fortunately, in my case, it added no benefit and so I happily plug straight into my HFC MC-6 Hemisphere line conditioner (which isn't current limiting) which then plugs straight into the wall.
