An adapter configured to transmit signal of the first electronic device to the second electronic device is provided. The adapter includes a first USB type-C controller, a second USB type-C controller and pleural USB type-C data transmission lanes connected to the second USB type-C controller and the first USB type-C controller. The second USB type-C controller is configured to: (1) obtain a first transmission specification supported by the second electronic device; and (2) transmit the first transmission specification to the first USB type-C controller. The first USB type-C controller transmits the first transmission specification to the first electronic device. The first electronic device transmits a control command to the first USB type-C controller according to the first transmission specification. The first USB type-C controller further uses a corresponding number of data transmission lanes according to the control command.