Abstract: An electrical plug connector assembly includes a socket connector and a plug connector. The socket connector includes a housing within which a U-shaped contact spring physically contacts a fixed contact part to establish an electrical connection. The U-shaped contact spring is disposed horizontally within the housing, in such a way that an imagined bending axis of the U-shaped contact spring lies parallel to the plug direction. The horizontal arrangement of the U-shaped contact spring within the housing makes it possible for the socket connector to have a relatively flat structure. A preferred application of such a plug connector unit is within a mobile telephone.