hey royb... i think my pup has a built in volt meter on the panel where my stereo is. i'll have to check this weekend when i open her up. as for the adapters, i'm using something very close to the small round block ones you posted. extension cord i'm using a standard one made for general outdoor use. i bet i'm not able to draw enough amps thru.
looking at my panel that feeds the outdoor receptacles it looks like they're only 15amp fuses. i notice that when i power on my tv it sometimes trips the gfci outlet. sounds like i got lots of things going on... lol