It’s not explicitly in the manual. It says “POWER Included Power Adapter 12V DC (positive tip), 2A, 100 to 240 Volts AC, 50/60Hz”. So I guess it’s 24W?
I checked with a kill-a-watt meter.
9.5W (in US using 110V & 60 Hz but that shouldn’t matter much).
Same power consumption if the GM is playing or just sitting idle. The volume control didn’t change the power either.