Electrical connector system

The present invention relates to an electrical connector system to provide network-transmitting channel. The electrical connector system including an outer circuit board, an electrical connector mounted on the outer circuit board, a transformer and a common mode rejection module mounted onto the outer circuit board and the electrical connector. The transformer is disposed in an insulative housing having a number of conductive tails. The common mode rejection module includes a magnetic core having two through holes and a dividing wall between the two through holes. The windings of the common mode rejection module wind around the dividing wall in a same direction and are electrically connected to the conductive tails of the transformer.