"the coffee gives me an energy" this articles gripe my soul:), energy has many sorts, mental energy, physical energy and so on, why "an" is incorrect?
No it doesn't. It's just an adenosine receptor inhibitor, which can make you feel more alert, but doesn't give you energy. (Actually, since most people don't drink straight black coffee, the sugar in the coffee would give you energy, but who cares? ツ)