From Brotato Wiki
Power Generator is an in-game item that can be bought from Shop or can be found in a Crate. Most Items increase the Stats of the player while some of them provide unique effects.
Power Generator is a unique item. Unique items can only be bought or found once per run.
Power Generator increases your % Damage depending on your Permanent speed stat. Temperary increases or descreases, such as the one granted by the Streamer's abilities, does not impact the number used for Power Generator. Once you have +25% speed or more, Power Generator becomes one of the most efficient ways to increase your % Damage.