Isn't it converting gasoline and oxygen into kinetic energy?

Turbochargers and such do add more oxygen to the engine, but but its not the extra oxygen thats adding the power. More oxygen in the combustion chamber means that you can add more fuel and its the increase in fuel which gives you power. Unless the air to fuel ratio is correct, the combustion wont happen properly or even at all. The cars computer uses the air flow sensor to determine how much oxygen is being sent to the engine and it compensates by adding the correct amount of fuel to keep the air fuel ratio correct.