An electrical connector system includes a substrate (1) connected to PHY side and an electrical connector (3) mounted on the substrate (1), a transformer (5) and a common mode filter (7). The electrical connector (3) is used to mate with a cable assembly and so forms a Cable side. The transformer (5) further includes a first wire (51) having two opposite ends electrically connected to the PHY side and a second wire (53) having two opposite ends. The common mode filter (7) has a third wire (73) and a fourth wire (75) that are physically separated from and electrically connected to opposite ends of the second wire (53).