A USB peripheral device with a power connector, such as a card reader, which serves as a peripheral device when it is connected to a host device such as a smart phone, while which can directly charge the host device when a charger is plugged in, is disclosed. The peripheral device has a USB connector and a controller. The ID, D+, D− and VBUS pins of the USB connector are connected to the controller and the power connector through a plurality of relays depending upon whether the power connector is connected by a charger or not. The peripheral device can be automatically switched to serve as a B-device or a power bridge transferring power from the charger to the host device.