Power is a game mechanic in most of the TRTF games.
In TRTF Classic
In it, the player has a set amount of power, which drains from 100% to 0. Lights, the camera, and the doors use power. If the power goes out, Freddy will arrive and attack.
In TRTF 2
In TRTF 4
Freddy Fazzy Funtime has limited power, and similarly to TRTF 2, you need to charge it up. Unlike TRTF 2, the generator is in the office, not in the cameras. The lever next to the cams is the one that charges the power. The power is displayed in a countdown at the bottom left of the screen. If the power goes out, Freddy will arrive, play a corrupted version of Toreador March, and attack. Freddy will kill you, since the Smoke is disabled when the power goes out.