If you hadn't turned on your system well before midnight when you did your test, it was probably just the sound of the gear finally having fully warmed up...
I don't think there's much doubt that PLC's can be beneficial for source compenents without downsides (I like balanced AC), but for power amps there's still debate and experimentation is probably in order. Even for source components, you have your advocates of parallel filtering and your advocates of in-line filtering and/or isolation transformers. If you decide the late night improvement you heard was the result of a reduction in powerline voltage flucuations, than you might want to investigate a PLC that performs active waveform/power factor correction. What I would say is that, if you have heard benefits from upgraded power cords, then you will likely hear benefits from a decent PLC.
I don't think there's much doubt that PLC's can be beneficial for source compenents without downsides (I like balanced AC), but for power amps there's still debate and experimentation is probably in order. Even for source components, you have your advocates of parallel filtering and your advocates of in-line filtering and/or isolation transformers. If you decide the late night improvement you heard was the result of a reduction in powerline voltage flucuations, than you might want to investigate a PLC that performs active waveform/power factor correction. What I would say is that, if you have heard benefits from upgraded power cords, then you will likely hear benefits from a decent PLC.