Embodiments of this application disclose an asymmetrical half-bridge flyback converter and a power supply system, to reduce a loss of the asymmetrical half-bridge flyback converter, and improve efficiency of the asymmetrical half-bridge flyback converter. The asymmetrical half-bridge flyback converter, including: a first power transistor, a second power transistor, a primary-side resonant capacitor, a transformer, a third power transistor, and a secondary-side resonant capacitor, where the first power transistor and the second power transistor are coupled to two terminals of a direct current power supply after being connected in series; and a primary side of the transformer is connected in parallel to two terminals of the first power transistor through the primary-side resonant capacitor, and a secondary side of the transformer is coupled to the third power transistor and the secondary-side resonant capacitor.