This disclosure relates to flyback transformer-based power converters that are capable of providing multiple output voltage levels. With respect to USB-PD adapter design, the flyback converter's output may be changed from 12V to 20V—based on the charging device's request. By using a bias circuit that monitors an output voltage level of the flyback converter, a bias voltage for the bias circuit may be determined to improve efficiency of the flyback converter. Embodiments include a comparator, microcontroller or switches to compare output voltage levels and provide bias voltages to the bias circuit.