Blowers/Superchargers make power from compressing air or air and fuel into the cylinders which gives it a larger fuel/air charge to fire on and actually to a point pushes the pistons where a normally aspirated engine has to draw the fuel/air into it which is drag. In other words the blower is kind of a compressor to a point but the boost or pressure is much less in most cases...a healthy stock engine can handle around 7 pounds of boost if its compression of the engine is not too high to start with. 7 pounds of boost may not sound like a lot but it adds loads of horsepower.
I wish I could find one that is like a Paxton for our truck that mounts like a alternator.