Bara has it right. No way it’s the wall side causing problems. Computers lock up, or suddenly restart when voltage drops below normal operating voltage. This is just some knowledge from being a computer tech for 15 years. That and overclocking before the introduction of auto overclocking on newer motherboards.
If the game isn’t locking up, or rebooting, the main voltage coming in isn't the problem.
Im not familiar with flipper fade or modern pins, but I highly doubt the board that drives the coils is bad on a newer game. Possible, but your flippers do work...so extremely doubtful.