Fixed.

I have a Dell XPS 13 (2016) with a Dell USB-C adapter. It will not detect my NEC LCD external monitor. I have tried a Dell USB-C adapter and a D-SUB cable to the monitor. I have also tried a Monoprice USB-C adapter with a Monoprice HDMI cable. Neither work. The monitor works fine with my Mac. I have told the computer to extend and duplicate the display using the Windows-P command. I have tried to update the driver for the monitor (I have NEC's driver), but it will not install because the monitor is not detected. Any help you can offer will be greatly appreciated.

Have you tried restarting your computer (restart option from the power icon) with the USB adapter disconnected. Wait until the computer boots up and is stable, then connect the adapter without the monitor connected to it. Do you hear the sound that indicates a USB has been connected? Then look in device manager (right click on the start icon and device manager will be one of the options) and are there any devices with exclamation points or unknown devices?

If all that looks normal, then connect the monitor.

Also, with the adapter connected, look in device manager under display adapters. If you see Microsoft basic display listed, right click on it and attempt to update the driver while connected to the internet.

Have you tried restarting your computer (restart option from the power icon) with the USB adapter disconnected. Wait until the computer boots up and is stable, then connect the adapter without the monitor connected to it. Do you hear the sound that indicates a USB has been connected?

Done, with sound heard.

[Then look in device manager (right click on the start icon and device manager will be one of the options) and are there any devices with exclamation points or unknown devices?

None that I could see and I opened all folders. Nonetheless, see below.

If all that looks normal, then connect the monitor.

Also, with the adapter connected, look in device manager under display adapters. If you see Microsoft basic display listed, right click on it and attempt to update the driver while connected to the internet.

The MS basic display adapter is listed, but has a triangle with an exclamation mark. I attempted to update it online, but was told that driver software for the device could not be located.

The MS basic display adapter is listed, but has a triangle with an exclamation mark. I attempted to update it online, but was told that driver software for the device could not be located.

That is more than likely the cause. I searched for drivers and couldn't find any. Do you have any other computers (even Windows 7 or 8) that this USB adapter does work on?

Maybe try this for a driver?
Windows

That is more than likely the cause. I searched for drivers and couldn't find any. Do you have any other computers (even Windows 7 or 8) that this USB adapter does work on?

Thanks for looking. I also couldn't find anything. FWIW, I also asked it to check and see if there were any updates and it says the system is current. No, this is the only Windows computer we have. The rest are Macs and are not new enough to have USB-C.

Also, you are connecting these adapters to a USB 3.0 port (blue) and not a USB 2.0 port (black)?

There are no colors on the USB ports with this computer. I have plugged it into what Dell says is the video out port. Left side. Also, it is the USB-C type - rounded corners.

There are no colors on the USB ports with this computer. I have plugged it into what Dell says is the video out port. Left side. Also, it is the USB-C type - rounded corners.

I realized that after I typed it :-). I didn't even know about USB-C until this thread.

The Monoprice website drivers webpage actually downloads the displaylink drivers - so maybe try the display link drivers.

I'll give them a try!

I was at Best Buy yesterday, so I thought that I would try one more thing and bought a cheapo HDMI cable for the Dell DA 200 adapter. I thought surely this won't work as the lower resolution, older, and presumably easier VGA didn't work with the adapter and the HDMI hadn't worked with the Monoprice cables and adapter, but it would be worth a shot. And, of course, it worked without a hitch. Why the others didn't work is beyond me. But thanks for the help NavyLCDR! I appreciate it.