From the Super Mario Wiki
Not to be confused with Big Amp.
New Super Mario Bros. U
In New Super Mario Bros. U, Bowser Amps make their only appearance in Red-Hot Elevator Ride as obstacles, where they electrocute the player upon contact. Unlike common Amps, Bowser Amps have special chains connected to another Bowser Amp, creating a stream of electricity to travel on the chains.
New Super Luigi U