From Brotato Wiki
Power Generator is a unique item. Only 1 of each unique item can be equipped, and it will then no longer be offered in the Shop, and no longer drop from loot crates.
Power Generator increases your % Damage depending on your Permanent speed stat. Temperary increases or descreases, such as the one granted by the Streamer or Golem'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.