In this article, the problem of hybrid optimal control for DC-DC power converters is treated. The designed control is of type bang-bang established from Pontryagin's maximum principle. The control is a state feedback and it is determined using an energy based minimization criterion derived from the power balance of Port-Hamiltonian systems. The developed control has the advantage to be easy to design and simple to implement in real time applications. The proposed control is applied to a SEPIC converter and validated in simulation and experimentation.