Abstract: A communications adapter card includes a circuit arrangement for causing an electrical voltage to be supplied to the card from a first voltage source, even if a second voltage source is available, and from the second voltage source if the first voltage source is not available. The circuit arrangement includes a Field Effect Transistor (FET) with its gate electrode connected to a control circuit which puts the FET in an off-state to inhibit the second voltage source from supplying voltage to the card if the first voltage source is available, and puts the FET in an on-state to supply voltage to the card if the first voltage source is not available. The invention makes it possible for a single communications adapter card to be used to attache power managed and non-power managed personal computers (PCs) to a Local Area Network (LAN).