We use the iPad as an EFB. We are only authorized to use the Apple charger plugged into the rear panel plug for charging, no other charging devices may be plugged into that receptacle.
About 1/2 of our busses have tablet interface modules (one per pilot below moveable window) with two USB ports, a main (2.1 amp) tablet charging port and an aux (~.3 amps) charging port for another device. These TIM's also allow for blue tooth connectivity to the aircraft, but this feature hasn't been exploited (nor do I think it will be)
The rest of our non Airbus fleet is being retrofitted with 110 volt plugs. The concern is in the future USB charging will go away.