An electronic device includes: a connector, arranged for coupling to a power supply external to the electronic device, wherein the power supply is arranged to provide a supply voltage to the electronic device to charge a battery of the electronic device; and a charger, coupled to the connector and selectively operated in a normal mode or a self-test mode, wherein when the charger operates in the normal mode, the charger is arranged for receiving the supply voltage via a power pin of the connector to charge the battery of the electronic device; and when the charger operates in the self-test mode, the charger provides a specific voltage to the power pin of the connector. The charger includes a detector to detect the current or voltage of at least one pin of the connector to generate a detecting result, and the supply voltage is set based on the detecting result.