The electrical connector system comprises 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 comprises 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) having a third wire (73) and a fourth wire (75) that are physically separated from the second wire (53). The third wire (73) has an end electrically connected to one end of the second wire (53) and an opposite end electrically connected to the Cable side. The fourth wire (75) has an end electrically connected to the opposite end of the second wire (53) and an opposite end electrically connected to the Cable side.