Running power through the Dual Dock's USB-C PD port is optional but is recommended for optimum performance. 

Having that this dock is "bus-powered" when attempting large file transfers (or using more than 2 ports on the dock) we recommend utilizing passthrough charging to keep your host device powered. 

Please note: Before plugging or unplugging your power cable, please ensure that all drives are ejected and the power switch is turned off before doing so.