This thing's awesome! how are you doing the different power ratings?
The power transformer I used has 0v, 190v and 275 v outputs. I used with a rotary switch : 190V and 275V to go in the circuit for the lowest power position, then 0 to 190 V for the second position and then 0v to 275v for the full 4/5 Watts.
The lowest position is enough for home use !