its also standby time. You can calculate the approx demand plus switched mode power supplies dont deliver over their rating and the texecom ones have issues anyway
It's highly unlikely its been well maintained, few people want any sort of manual for anything that is. However assuming it hasn't been well maintained I'd go with Mr h's findings
It's not dc a speaker needs ac. I wouldn't by choice run speakers with anything else. Speakers and drivers can be very electrically noisy.
You will probably get away with it but still