NOVELTY - The method involves determining (S100) a connectivity state of an auxiliary power source with an energy storage device. The connectivity state of a load with a fuel cell system is determined (S200). The power adapter operation mode is selected based on connection states of the auxiliary power source and load (S300). The auxiliary power source is connected to an energy storage device and load is connected to the fuel cell system. The power is provided from the auxiliary power source to the load. The power is generated from fuel by a fuel cell stack. The generated power is provided to the load.    USE - Method for operating a power adapter (Claimed), such as an energy storage device, fuel cell system with fuel supply and fuel cell stack for a load, such as portable consumer device, mobile phone, tablet, laptop, electric vehicle, unmanned aerial vehicle or any other suitable load, particularly for managing a fuel cell system in a fuel cell field and determining cartridge fuel production.    ADVANTAGE - Usage of multiple power sources is improved. Fuel cell system start-up is facilitated. Fuel cell system operation is facilitated after the power adapter is disconnected from the auxiliary power source. Cooling the fuel cell system is facilitated. User handling is facilitated. Automatically determines the suitable operational mode by power adapter is ensured. Automatically exchange the consumed cartridge for a fresh cartridge is ensured. Portability of the fuel cell system is facilitated. Carbon footprint is reduced. Fuel flow to the fuel cell stack is facilitated. Wastage of heat from the fuel cell assembly is reduced.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a power adapter for a load.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart of a power adapter operation method.    Determining connectivity state of auxiliary power source with a power adapter (S100)    Determining a connectivity state of a load with the power adapter (S200)    Selecting the power adapter in an operation mode based on the connectivity state of the power adapter (S300)    Operating the power adapter in auxiliary mode (S320)    Operating the power adapter in fuel cell mode (S340)