USB won't work on XPS 12 9250 with Dell Adapter USB Type C to HDMI/VGA/Ethernet/USB 470-ABQN

I have an XPS 12 9250 with an external Dell Adapter USB Type C to HDMI/VGA/Ethernet/USB 470-ABQN.  This adapter is working for Ethernet and VGA, but the USB port is not working.  I suspect that I need the correct drivers installed.  When I plug in my windows phone or my android phone, both devices show that they are charging, but windows 10 does not indicate that it sees the devices.  If I plug in an external keyboard to the adapter's USB port, windows 10 does not react, and the keyboard lights do not come on (keyboard works fine on 2 other computers).

So, I'm pretty sure I've installed all the latest drivers that are listed on support.dell.com for the xps 12 9250, but it's hard to tell as there seem to be scores of them.

Is anyone else having this problem?  Can anyone tell me which specific drivers I need to get USB working?  Thank you