Regulated power supplies are rarely used in amplifiers and the voltage on the rails is direclty proportional to the voltage on the AC.
Having said htat, that's an unusually high drop. Your house's age may have something to do with this but modern code has a separate circuit just for the microwave. If you are still seeing that kind of drop, measure the neutral to earth. If it's more than 2V you have a separate issue which is a bad neutral. I use these because they do both voltages at the same time.
HJaving said all of that I use a Furman voltage regulator to keep my AC within 5V at all times, but it's not for bad wiring. It's for the 2 heat pumps turning on and off and seasonal variations.