An adapter, comprising: an adapter interface (121, 41) configured to be connected to a battery pack capable of being detachably connected to a power tool; and a direct current interface configured to be capable of being selectively connected to an external power consumption device or an external power supply device, wherein an output or input power of the direct current interface is greater than 10 W; wherein the adapter further comprises a voltage conversion circuit, a communication module, a main controller, and a two-way power supply controller; wherein the voltage conversion circuit is connected in series between the direct current interface and the adapter interface, wherein the voltage conversion circuit is configured to convert electric power of the external power supply device into an electric power output adapted to the battery pack; or the voltage conversion circuit is configured to convert electric power of the battery pack into an electric power output adapted to the external power consumption device; the communication module is configured to be capable of sending a control signal to a main controlling module according to a signal state of the direct current interface; and the main controller is connected between the direct current interface and the adapter interface, the two-way power supply controller is connected between the main controller and the voltage conversion circuit, and the main controller is configured to control a current direction and an output voltage of the voltage conversion circuit according to the signal state of the direct current interface and a signal state of the adapter interface so that the external power supply device charges the battery pack or the battery pack is discharged to supply power to the external power consumption device. an adapter interface (121, 41) configured to be connected to a battery pack capable of being detachably connected to a power tool; and a direct current interface configured to be capable of being selectively connected to an external power consumption device or an external power supply device, wherein an output or input power of the direct current interface is greater than 10 W; wherein the adapter further comprises a voltage conversion circuit, a communication module, a main controller, and a two-way power supply controller; wherein the voltage conversion circuit is connected in series between the direct current interface and the adapter interface, wherein the voltage conversion circuit is configured to convert electric power of the external power supply device into an electric power output adapted to the battery pack; or the voltage conversion circuit is configured to convert electric power of the battery pack into an electric power output adapted to the external power consumption device; the communication module is configured to be capable of sending a control signal to a main controlling module according to a signal state of the direct current interface; and the main controller is connected between the direct current interface and the adapter interface, the two-way power supply controller is connected between the main controller and the voltage conversion circuit, and the main controller is configured to control a current direction and an output voltage of the voltage conversion circuit according to the signal state of the direct current interface and a signal state of the adapter interface so that the external power supply device charges the battery pack or the battery pack is discharged to supply power to the external power consumption device.