Power pumps?

So I need to increase my supply! Baby girl has upped her need for milk and when I pump I don't seem to be able to keep up. I've read about the miracles of power pumps. Has anyone tried this and had it work? How much did it increase your supply? And do I need to do the power pump at any particular time during the day? For example: if I need to produce more milk in the afternoons, do I need to power pump in the afternoon for my supply to respond and increase at that time? Thanks for any help you all can offer!