Power comes from two things, shoulder turn and wrist break
Complete your shoulder turn for your full power and complete your wrist break so that you have a right angle between the left arm and club as in the picture above.
Your left shoulder should be under your chin at the top of the backswing.
Place your golf club across your shoulders in your address position and turn until your club is perpendicular to the target.
This gives you the feel of the full shoulder turn you need to achieve your maximum power.