A super-charger performs the same function as a turbo-charger, in that it forces more air into the engine, and therefore generates more power.
The difference is that where a turbo-charger is powered by the car’s exhaust gases a supercharger is powered mechanically by the engine.
In essence, the super-charger is a small turbine that sits in the engine’s air intake, and is connected to a pulley on the outside of the engine by a rod. This pulley is linked by a belt to a similar pulley on the end of the crank.
When the engine runs, the crank turns, thereby spinning the supercharger, which draws in air, compresses it and injects it into the cylinder. There are pluses and minuses to super-charging.
On the positive side, response is instant when you press the accelerator because it’s attached by a solid mechanical link; therefore there’s no need to wait for the engine to generate enough exhaust gases to spin the turbine, so no ‘lag’.
However, this mechanical link also creates a burden on the engine, which means that while low- and medium-rev responses are instant, ultimate power can be curtailed simply due to the frictional losses that are inherent in the system.
Simply put, you need a bigger super-charger to get the same power output as a turbo, but of course a bigger super-charger generates more frictional losses, so you face the law of diminishing returns.
Super-chargers tend to work better on larger engines, where the ‘drag’ they create is much more easily overcome by the large torque output of the motor.
In addition, as with a turbocharger, the extra air it injects into the engine is nothing without extra fuel to burn.
However, the extra ‘drag’ on the engine from the super-charger means that even more fuel is required. So, super-charging is certainly a way to get more power, but it isn’t as efficient as turbo-charging.