Is there a dual 120V to NEMA 14-50 adapter available? I can't seem to find one. If so, does anyone have any experience with it using the UMC? How many miles (or kW) per hour of charge do you get? This would seem to be a better choice rather than plugging into the standard 120V alone when other faster charging options are not readily available, such as at a friend's or relative's house.