Also known as a “blower”, but not to be confused with a turbocharger (which is exhaust-driven).

A supercharger is essentially an air pump driven off the engine’s crankshaft, enabling high-pressure air to be forced into the engine, thereby boosting the charge and greatly increasing power output.

In terms of power, there are some mechanical losses through being driven off a belt from the crankshaft, but this is greatly offset by the extra charge itself and the fact that the extra power is available from low revs.