That is a Thunderbolt dock, and nothing in the manual for the Vostro 3425 mentions it having a Thunderbolt port. There's also no mention of support for USB-C alternate (displayport alt mode) in the system manual, so if your goal is video output in this system, you need to use a direct connection from the HDMI port to the monitor.  
Vostro 3425 with USB-C dock: display not working We just purchased the Vostro 3425 and docking station. But the external display does nothing. The dock seems to work fine, Dell K20A001. Keyboard and mouse work fine connected to the dock. But the display does nothing, the Vostro does not find a connected display. Tried other docks, HDMI and DVI cables, updated BIOS and all drivers, windows updates, several reboots. Still no display found. Any ideas? Thanks Richard.  
Vostro 3425 with USB-C dock: display not working