Today academic and industrial research is addressed on fuel cell based power supply to replace current lithium-ion and similar rechargeable battery systems. For system simulation, fuel cell models are developed. Even if power electronics designers demand for a black-box model to limit the knowledge of physical and chemical parameters, high performance in terms of model accuracy and portability is absolutely necessary. A steady state and dynamic fuel cell model oriented to power supply systems design is proposed and, as an example, the implementation on PSIM software is presented. Simulation and experimental results are compared and the model portability is discussed.