Litnin I think you missed the point/are confusing efficiency with overall power production.

By your logic (energy taken directly from the engine cannot create energy) a supercharger will not work. Of course in reality they do work. They work to create more power by allowing more fuel to be pumped through and burned to match the greater air being delivered. Hence more power is created. Granted it is at a lower efficiency. However more total energy is created and delivered to the wheels.

A leaf blower (i.e. electric supercharger) would have even a greater inefficiency as you have to convert mechanical energy to electrical energy back to mechcanical energy to move the air. Again though just because it is less efficient doesn't mean it couldn't deliver more power. Granted a less efficient power but more power than the engine otherwise would deliver.

I do though agree that such a system is not worth much. I just fail to see that much of a power gain and too many costs (including more fuel) and things to go wrong for such a system to be worth it.