Low AC Line Voltage

Hello all.

I had something very strange happen the other night. My system hasn't been sounding quite right so I decided to try some power cords. I tried 3 Cardas Cross power cables. One on my power amp, one on my preamp and one on my Oppo CD player. I connected them all to an outlet box I had assembled using hospital-grade hardware. I turned everything on and let it warm up for a bit and the sound was totally unbelievable. Big wide open warm detailed spacious deep everything you could possibly ask for. I was totally amazed. The next morning I turned everything back on and tried it again and all of that wonderful sound was gone. It was almost like I had dreamed it. The system was back to sounding harsh and just not fun again. I couldn't figure out what happened. It was that way for several days. I bought a plug-in voltage meter. The voltage is always about a hundred 116 volts or so. This morning it was 123 volts and that wonderful sound was back. Am I crazy or could this possibly be caused from voltage?

Thanks in advance.

Ben