An example controller for a flyback power converter includes a secondary-side circuit comprising a secondary-side controller. The secondary-side controller is configured to sense an electrical characteristic of a secondary-side output of the flyback power converter, select, based on the sensed electrical characteristic, a power mode, and transmit, over a communication channel, a control message specifying the selected power mode. A primary-side circuit of the controller includes a primary-side controller. The primary-side controller is configured to receive, over the communication channel, the control message specifying the selected power mode and control primary-side flyback drive circuitry of the primary-side circuit to drive a primary-side output of the flyback power converter according to the selected power mode so as to control a value of the electrical characteristic of the secondary-side output of the flyback power converter.