The invention is applicable to the field of household appliances, and provides a positive-negative automatic conversion circuit and a power output module. The positive-negative automatic conversion circuit comprises a first diode, first and second electrodes which are used for accessing a direct-current power supply, a relay, an absorption circuit which is connected between a first end and a second end of a coil, a positive output electrode which is connected with a first normally closed contact and a second normally open contact, and a negative output electrode which is connected with a first normally open contact and a second normally closed contact. Polarity conversion is realized by the relay. The relay is equivalent to any impedance when switched on, and the input voltage and output voltage are basically unchanged, so that there is no loss. Therefore, a lossless polarity conversion function is achieved.