A head-mounted display system , comprising: a head-mounted display gear ; and a host ; characterized by: a first Universal Serial Bus, USB, Type-C transmission line coupled between the head-mounted display gear and the host for transmitting power, data and a video stream; a second USB Type-C transmission line coupled between the head-mounted display gear and the host for transmitting the power, the data and the video stream; and the host comprising: an input/output interface comprising: a first transmission port arranged to accommodate the first USB Type-C transmission line ; and a second transmission port arranged to accommodate the second USB Type-C transmission line ; and a dual-power judging circuit configured to: determine whether the first USB Type-C transmission line is plugged into the first transmission port; determine whether the second USB Type-C transmission line is plugged into the second transmission port; and allow the host to charge the head-mounted display gear only when determining that both the first USB Type-C transmission line and the second USB Type-C transmission line are plugged into the input/output interface . a head-mounted display gear ; and a host ; characterized by: a first Universal Serial Bus, USB, Type-C transmission line coupled between the head-mounted display gear and the host for transmitting power, data and a video stream; a second USB Type-C transmission line coupled between the head-mounted display gear and the host for transmitting the power, the data and the video stream; and the host comprising: an input/output interface comprising: a first transmission port arranged to accommodate the first USB Type-C transmission line ; and a second transmission port arranged to accommodate the second USB Type-C transmission line ; and a dual-power judging circuit configured to: determine whether the first USB Type-C transmission line is plugged into the first transmission port; determine whether the second USB Type-C transmission line is plugged into the second transmission port; and allow the host to charge the head-mounted display gear only when determining that both the first USB Type-C transmission line and the second USB Type-C transmission line are plugged into the input/output interface . a first Universal Serial Bus, USB, Type-C transmission line coupled between the head-mounted display gear and the host for transmitting power, data and a video stream; a second USB Type-C transmission line coupled between the head-mounted display gear and the host for transmitting the power, the data and the video stream; and the host comprising: an input/output interface comprising: a first transmission port arranged to accommodate the first USB Type-C transmission line ; and a second transmission port arranged to accommodate the second USB Type-C transmission line ; and a dual-power judging circuit configured to: determine whether the first USB Type-C transmission line is plugged into the first transmission port; determine whether the second USB Type-C transmission line is plugged into the second transmission port; and allow the host to charge the head-mounted display gear only when determining that both the first USB Type-C transmission line and the second USB Type-C transmission line are plugged into the input/output interface . a first transmission port arranged to accommodate the first USB Type-C transmission line ; and a second transmission port arranged to accommodate the second USB Type-C transmission line ; and a dual-power judging circuit configured to: determine whether the first USB Type-C transmission line is plugged into the first transmission port; determine whether the second USB Type-C transmission line is plugged into the second transmission port; and allow the host to charge the head-mounted display gear only when determining that both the first USB Type-C transmission line and the second USB Type-C transmission line are plugged into the input/output interface . <EOS>