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.

Yes, pigtail the blacks. Take two short pieces of black wire and wirenut them to the power. Then attach a resulting black to each dimmer.

Note that when you put two dimmers in a box, you usually have to remove a side. This reduces the rating of the dimmer. See the instructions.

OK... thanks, what do you mean though by reduce the rate of the dimmer and remove a side... remove the side panel of the box?

The dimmer plate is designed for a single gang box to get the maximum heat sink area under the plate.

Usually when you put two of them side by side in the same box, they won't fit.

So, they are designed, so the sides of the heatsink can be removed.

If you had a 500 W dimmer, with one side removed you might get 400 W and with 2 sides removed you might get 300 W of capabiliy . Check the directions.