Ernie Els' tag as "The Big Easy" certainly fits. Yes, he's a big guy and, yes, his swing looks as smooth as silk. But make no mistake — Ernie hits the ball hard. He's the poster child for torque and leverage (the two swing traits that allow you to add power without swinging harder).
I've known Ernie for almost 20 years, and I can tell you that the way to generate his effortless power and accuracy is in your wrists. Notice how he hinges them quickly and fully as he swings the club to the top. When he lets the hinge out, it gives the appearance of swinging smoothly and without effort, even though his clubhead is blasting through impact at 120 mph.
You should mimic his hinge, but don't copy it move-for-move. Ernie cups his left wrist at the top and releases the club very late. He does this to fight his tendency to hook the ball under pressure. You'll do better with a flat left wrist at the top and a strong release once your hands reach the hitting zone. But if you want more swing speed or a few more yards off the tee, Ernie's moves are the keys you've been seeking.