A system having a screen, in particular a flat screen, and having an external power supply unit that can be connected by a plug connector to the screen in order to supply the screen with a DC voltage. The system provides a signaling device at the power supply unit end and a comparator at the screen end for comparison of the operating parameters of the power supply unit with nominal operating parameters. A fault signaling device is provided for indicating unacceptable discrepancies between the signaled operating parameters and the stored operating parameters.