A hybrid power supply includes a fuel cell and an interface between the fuel cell and a fuel cartridge or external battery and a switching type DC/DC boost type converter that receives energy from the fuel cell or external battery and is arranged to deliver the energy to a rechargeable cell. The hybrid power supply also includes a fuel cell current sensor/comparator, included in a feedback control loop disposed about the DC/DC converter, which controls in part operation of the converter to provide constant current discharge on the fuel battery side of the hybrid power supply. An adapter that couples a source of AC power such as a charger to the interconnect is also disclosed.