If I want to train for more power where the Squat is concerned, I wouldn't simply do normal back squats all the time. I would need to become more explosive. Power is how fast I can move a certain weight. I like two modes of training when talking about gaining power for your squat, they are Rate of Force Development (RFD), and Elastic Explosiveness (EE). RFD is the ability to accelerate from a hard stop or standstill. EE is not the use of elastic bands, although I do love that training as well. EE is talking about muscle elasticity. It is the ability to generate force from the stretch shortening cycle through a countermovement. My two favorite examples of these are the box squat and the seated jump. If you are unfamiliar with either of these, the box squat is doing a normal squat down to a box or bench, completely relaxing (as much as possible) and then exploding up to standing. The seated jump is similar, you start seated on a bench or box or even a chair and you explode up jumping as high as you can. Another one that I really like is the speed squat. Which is simply as it sounds. You are doing a lighter weight (generally half or less of your max), and you are doing reps down and up as fast as you can. I generally do this in conjunction with a set of normal heavy squats, like a superset.