Morley Hum Exterminator. It plugs into the wall between the outlet and your amp and targets AC line hum and buzz — the ground-related kind that follows you around a room and has nothing to do with your guitar or your cable. Rated AC 120V 60Hz, 720W, 6A max, so it will handle an amp comfortably.

Worth being straight about what it does and does not do: it addresses hum and buzz coming in on the AC line. It will not quiet single-coil pickup hum, a noisy pedal, hiss, or anything generated downstream of the outlet. If your noise problem is the room's wiring, this helps. If it is your pickups, it will not.

Simple thing, no controls, nothing to set.

Cosmetically used — handling marks on the housing, prongs are straight and clean. Nothing cracked.

I have a second one of these listed separately. Message me if you want both.