You're overdriving the gate of the triac (assuming the triac terminals are all connected properly, not labeled on your diagram). Recommend a 560 ohm resistor in series with the switch, using your attached circuit topology. Can't say how that explains the voltage rise for sure, but it's a good place to suspect what's causing the problem.
But, yes, why not just connect the switch with a series resistor between the gate terminal and the T2 terminal of the triac and forget the power supply?