An energy harvesting system that scavenges on-board train vibrations to supply a DC load is here presented. The developed system benefits from an electronic interface, which is equipped with a Maximum Power Point Tracking (MPPT) controller to maximize the power extraction. In particular, the train suspension vibration is mechanically converted into a unidirectional rotation of a shaft by a rack and pinion system equipped with a Mechanical Motion Rectifier. The unidirectional rotating shaft drives a three-phase electromagnetic generator whose AC voltages are rectified by an electronic interface, which also maximizes the extracted power. Indeed, the time variability of the train suspension displacement leads to a time-variable generator speed, which requires a dynamical adaptation of its load to maximize the power generation. To this aim, a MPPT controller based on a Perturb and Observe (P&O) technique with current limitation is employed. Experimental results show the ability of the proposed power electronic interface to maximize the power extraction in presence of both constant and time-variable generator speeds.