The invention provides for a network power-supply voltage adaptor arranged to receive an input voltage (V in) from a network trunk cable and to present an internal voltage derived from the said input voltage (V in), the adaptor being arranged, when at least one of the input voltage (V in) or the said internal voltage is above a reference voltage (Ref V), to regulate the received input voltage (V in) to provide an adaptor output dc power supply voltage (V out) at a substantially constant dc power supply level less than that of the input voltage (V in), and independent of changes in the input voltage level (V in), and the adaptor further comprising at least one communication feed-through loop (55, 56, 66, 68) for the passage of substantially unaltered communications signals through the adaptor.