A power supply, comprising: power circuitry configured and operative to provide DC power to a separate load via a pair of conductive terminals (+,-) of the power supply, the power circuitry including (i) basic power supply circuitry, and (ii) a power switching transistor in series between the basic power supply circuitry and one of the conductive terminals (-), the power switching transistor being closed when the power supply is delivering power to the load; a signal-forming resistor (Rchk); and a controller configured and operative to conduct bidirectional communications with the load via the pair of conductive terminals and to generate load-dependent values of configuration parameters of the power supply in response to the communications, the bidirectional communications including (i) in a transmit mode, supplying a pulsed binary control signal (Q1_ON) to the power switching transistor to convey an outgoing message to the load as a sequence of distinct signaling voltage values across the pair of conductive terminals, and (ii) in a receive mode, maintaining the power switching transistor open and monitoring a signaling voltage (Vx) to receive incoming messages from the load as a sequence of distinct voltage values developed by the signal-forming resistor in response to corresponding signaling current values generated by signaling action of the load; the power supply characterized by the signal-forming resistor (Rchk) being connected in parallel with the power switching transistor and in series between the basic power supply circuitry and the one conductive terminal, the signal-forming resistor providing a path for signaling current conducted by the load and developing a corresponding signaling voltage (Vx) at the one conductive terminal (-) when the power switching transistor is open, the signal-forming resistor having a resistance value to limit the outrush current conducted by the load from the basic power supply circuitry to substantially less than a maximum current that the power supply can provide, when the load is first applied with the power switching transistor open and the power supply having a maximum output voltage. power circuitry configured and operative to provide DC power to a separate load via a pair of conductive terminals (+,-) of the power supply, the power circuitry including (i) basic power supply circuitry, and (ii) a power switching transistor in series between the basic power supply circuitry and one of the conductive terminals (-), the power switching transistor being closed when the power supply is delivering power to the load; a signal-forming resistor (Rchk); and a controller configured and operative to conduct bidirectional communications with the load via the pair of conductive terminals and to generate load-dependent values of configuration parameters of the power supply in response to the communications, the bidirectional communications including (i) in a transmit mode, supplying a pulsed binary control signal (Q1_ON) to the power switching transistor to convey an outgoing message to the load as a sequence of distinct signaling voltage values across the pair of conductive terminals, and (ii) in a receive mode, maintaining the power switching transistor open and monitoring a signaling voltage (Vx) to receive incoming messages from the load as a sequence of distinct voltage values developed by the signal-forming resistor in response to corresponding signaling current values generated by signaling action of the load; the power supply characterized by the signal-forming resistor (Rchk) being connected in parallel with the power switching transistor and in series between the basic power supply circuitry and the one conductive terminal, the signal-forming resistor providing a path for signaling current conducted by the load and developing a corresponding signaling voltage (Vx) at the one conductive terminal (-) when the power switching transistor is open, the signal-forming resistor having a resistance value to limit the outrush current conducted by the load from the basic power supply circuitry to substantially less than a maximum current that the power supply can provide, when the load is first applied with the power switching transistor open and the power supply having a maximum output voltage.