I have pretty poor electrical voltage stability in my neighborhood. The power company is aware and admits that the local grid is a bit "overloaded". (There is a plan to fix it... but I've been hearing that for 10 years...)
I installed a PS Audio regenerator, and I can tell you it is effective for dealing both high noise in the AC line as well as moderate swings in external voltage. Sonically, the immediate impact was the system sounded more "relaxed" and not straining to handle big dynamic swings in the music. I have everything plugged into it, sources, preamp, dac, and power amps.