A wall plate assembly includes a wall plate with an insertion slot for the installation of a HDMI (High-Definition Multimedia Interface) connector of a HDMI cable, a signal amplifier connected to the back side of the wall plate for receiving the installed HDMI connector and amplifying the signal, and a support device, which comprises a vertical support frame vertically adjustably fastened to the wall plate below the insertion slot and a horizontal support frame horizontally adjustably fastened to the vertical support frame for holding down the installed HDMI connector on the vertical support frame.