An electronic transformer (100) and a microwave cooking appliance (200). The electronic transformer (100) comprises a rectifier module (10), a transformer (20), a switch module (30), and a control module (40). The rectifier module (10) is connected to an alternating current source (50); the transformer (20) is connected to the rectifier module (10); the switch module (30) is configured to provide an on/off signal to the transformer (20); the control module (40) is connected to the switch module (30); the control module (40) is configured to generate a control signal according to preset power and provide the control signal to the switch module (30) so as to control the switching frequency of the switch module (30).