The present document contains requirements for: - the output performance of the direct current (dc) power equipment at the interface "A"; - the input of the telecommunications equipment connected to interface "A" powered by dc. The dc voltage at interface "A" may be derived from the AC primary supply. The dc supply may incorporate a backup battery. If any other equipment e.g. datacom equipment, are connected to interface "A" in parallel to telecommunications equipment, all requirements addressed in clause 4 of the present document must be fulfilled. The present document aims at providing compatibility between the power supply equipment and the power consuming telecommunications equipment, and also between different system blocks connected to the same power supply.