A power supply control device comprises a controller and power connection circuitry. The power connection circuitry comprises a switchable power connection path between a source side and a load side. The power connection path is switchable to operate in a first operation state or an on-state in which state impedance between the source side and the load side is very low to permit flow of operation current through the power connection path, or a second operation state or an off-state in which state impedance between the source side and the load side is very high to impede flow of operation current through the power connection path. The controller is to operate to transmit at least one type of enquiry signals to the load side and to determine with reference to at least one type of received responsive signals whether a load on the load side is eligible for power supply connection. The controller is to switch the power connection path to the on-state or to maintain the power connection path to the on-state if the responsive signals indicate eligibility for power supply connection.