Not talking about the signal.. talking about the wall wart itself.
Fueling my closet love of 80s and 90s rack gear, I recently got a Lexicon Vortex on the cheepz, but no adapter. Bought a 3rd party one.
Worked fine the first day. Was gone to NYC for 2 days, came back and turned the power strip it was plugged into on, and it started buzzing. Oddest thing ever. Thought the damn thing was gonna blow up. It was powering the unit just fine, and no extra audio noise in the signal chain, it's just that the wall wart itself has a buzz coming from it.