A switching power supply, with or without a secondary side controller, is connectable to a power-supply-using device (such as a printer without a power supply) receiving a voltage from the power-supply's secondary side. The device has a device controller (such as a printer controller) which controls the device, wherein the power supply is adapted to receive a power-supply control signal or power-supply control data from the device controller. A method for operating the switching power supply includes using the power-supply control signal or the power-supply control data to generate an input control signal for the power supply's primary side controller. A device-and-power-supply assembly (such as a printer) includes a switching power supply lacking a secondary side controller and includes a power-supply-using device having a device controller (such as a printer controller) wherein the power supply is adapted to receive a power-supply control signal from the device controller.