I have 2 of these. One in my truck and one in my office.
It is a 24V (40VA) transformer w/ a 3.5 amp circuit breaker. Bought the box from Radio Shack, transformer/circuit breaker from a local hvac supply house, and picked up the #16 wire scrapped on a jobsite. I used an old 12' extention cord I found lying around. It has 4 outlets.
I thought about using a multi-tap transformer(120/208/240/480) and alligator clips in places where a 120v receptacle was not accessable. You could use power from a disconnect both 480/240V. I just haven't gotten around to that yet.JUST BE VERY CAREFUL!
I'm not sure on the power rating of the VAV's but it works on control modules just fine.