A method of operating a power adapter that includes an energy storage device and a fuel cell system including a fuel supply and a fuel cell stack, the method including determining a connectivity state of an auxiliary power source and a load with the power adapter, and selecting a power adapter operation mode based on the connection states of the auxiliary power source and the load. The operation modes of the power adapter include at least an auxiliary mode when the auxiliary power source and the load are connected to the power adapter, and a fuel cell mode when the auxiliary power source is disconnected from the power adapter and the load is connected to the power adapter. The auxiliary mode includes providing power from the auxiliary power source to the load, and the fuel cell mode includes providing fuel cell power to the load.
