USB charger apparatus and chargeable electronic devices are presented in which the device and charger use USB cable data lines to establish a bidirectional communications connection, and the charger provides charger capability information to a master controller of the electronic device via the communications connection. The device controller preferentially selects a fastest charging match between the charger capability information and device charging capability information, and sends configuration information through the communications connection to set the power supply level of the charger. The charger communicates power supply status information to the electronic device, and the device can reconfigure the charger power supply level accordingly.