I have one 12/2 wire coming into a box. It is on a 20 amp circuit. I have 4 recessed lights that I want to run off one dimmer switch and another light I want to run off another dimmer switch all in the same box. Can I attach 2 blacks to the first switch and then with the extra black, run that to the second switch? Do I have to run 2 different power supplies? Please help... I am experiencing much difficulty answering this question.