A mains power adaptor (1) incorporating a fuel cell (5) for providing alternative power to a low voltage portable device when no mains power is available. The adaptor (1) includes electrical pins (4) configured to connect with a mains power supply socket; a power converter circuit (7) having an input coupled to the electrical pins (4) for converting mains power to a lower voltage supply (8); an electrical output (2) of the lower voltage supply (8); and a fuel cell (5) switchably coupled to said electrical output. The adaptor (1) has a fluid connection port (12) for coupling a fluid fuel outlet of a fuel cartridge (not shown) to a fuel inlet of the fuel cell (5) and the fluid connection port (12) is disposed in a face (3) of the adaptor (1) from which the electrical pins (4) extend. A valve of the fuel cartridge is operable by engagement with the electrical pins (4) of the adaptor (1).