Hi,
This is what the dimmer says s how to connect it.
Connection Instructions:
Red wire is positive and the black wire is negative, both are output connect to the LED; brown wire is positive and the blue wire is negative, both are input connect to the power supply.
I would not even trust the unit at all, when the seller knows nothing about AC or DC.
The dimmer pot, could be at any potential, even at mains potential.
Can you tell us your electronics, programming, arduino, hardware experience?
Thanks.. Tom.. 