Every component in an audio system is sensitive to AC polarity. Ensuring that your electronics are connected to the AC line with the correct polarity is essential if you want to realize the full potential of your system.
Some believe Correct AC Polarity is related to lower Chassis Voltage when the ground lifted but There is no need to measure the Chassis Voltage (to Ground Potential) because in some rare instances, the higher reading Voltage will produce better sound from the component. the best way is listening and detecting the Correct AC Polarity.
Plug the component into the wall socket and turn on the power switch. Listen to Music, then Unplug the component from the wall socket, Reverse the position of the plug in the wall socket and repeat Listening.
The correct A/C alignment will be the one that gave the best sound.