Many of the "jump starter" battery packs (per above) advertise 2nd generation "smart" chips for the USB outputs. They claim to provide up to 2.1amps to pretty much any device that supports/negotiates it. Plus the 19V output for direct connection to a notebook's charger input.

Dunno how well any of that works, but they do work well for starting impossibly large engines with dead primary batteries in the dead of winter here.