Buy a digital oscilloscope for under $400 and learn how to use it. Way more informative and useful, way less woojum.
How noisy is my line? Audio Prism Noise Sniffer
A friend and audio journalist had this Prism device, and he plugged it into various outlets when I visited him. It gave a clear sense of which outlets were noisy and how effectively his conditioners were helping with noise.
He said these were not made any longer. Does anyone know of another tool like this?
It seems like it could save someone with clean power (or a quiet outlet) a lot of money from conditioners/regenerators which would not necessarily help.