Method and apparatus for supplying power to a connection device

The present invention concern a method and an apparatus for stabilizing power supply to a connection device, such as an ONU. The power is supplied via wires, such as telephone wires, using DC voltage and the wires having a first conductor, such as a ring conductor and a second conductor, such as a tip conductor. The currents in the first conductor and in the second conductor are measured and if a difference between the currents is detected as being above a first threshold value the supplied DC voltage will be lowered. Despite the instruction to lower the supplied DC voltage the currents in the first conductor and in the second conductor are continuously measured. Within period of time, e.g. 5 ms, since it was detected that the difference between the currents were above the first threshold value it is decided if the difference between the currents are below a second threshold value and/or if the difference between the currents is diminishing faster than a rate threshold value. If any or both of these criteria are fulfilled the controller is configured to instruct the converter to increase the supplied DC voltage.