From the Super Mario Wiki
Bowser Amps are a special type of Amp that first appear in New Super Mario Bros. U. As their name implies, they resemble Bowser's head.
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
The Bowser Amps reapear in New Super Luigi U in the Peach's Castle level Current Event where they are a major obstacle.