This paper proposes a power decoupling three-port converter to integrate the on-board charger and on-board auxiliary power module. A shared switching leg is employed to provide an extra degree of freedom to regulate the output power of different ports. Hence, control decoupling can be achieved even if all ports operate at the same time. In addition, a four-leg integrated matrix transformer is also provided to reduce the losses of the magnetic component. A comparison between the discrete and the integrated transformer is offered, and the employment of the integrated transformers can effectively reduce the core losses under different output conditions. Experimental validation is tested on an integrated 6.6 kW + 3 kW prototype.