An adapter connection structure, which includes a first converter and a second converter. The first converter is connected to at least one input terminal to receive an input power and converts the input power into a transitional power. The second converter is connected to the first converter via a transit cable to transmit the transitional power, converts the transitional power into a DC output power and outputs the DC output power via a DC power cable. As the transitional power transmitted from the first converter to the second converter is in the form of a high-voltage and high-frequency AC power or a high-voltage DC power, the power transmission loss in the transit cable is reduced. Therefore, the present invention reduces transmission loss.