Where does the power in golf come from down swing or back swing?

Well, if by "back swing", you refer to the rest of your swing after hitting the ball... then it's probably down. Also, I've never seen someone hit the ball away from the hole to make it go towards the whole... be neat though. Anyway, I'm no expert, but I'd really say that, yeah, it's the "down swing". Just make sure to also then move it foreward to hoit the ball.