C5522QT, connecting to Optiplex setup

Posting this so the next person doesn't have to go through the problems I had.

We purchased a C5522QT touchscreen monitor and a companion OptiPlex 7090 mountable mini-PC.

The set-up instructions do not really describe how to connect the PC to the monitor correctly (or even at all).

For the touchscreen to work, the USB 3.0 SS cable (Dell calls this the "upstream data connector", it has an A-type connector on one end and a pyramidal connector on the other end) must be connected from the PC (A-type) to the monitor (pyramidal type). In particular, on the monitor there are three possible connectors. You must connect the cable to the connector that corresponds (and is next to) the video input connector you are using. There is a printed line on the monitor that indicates which USB upstream cable connector matches each video input connector. If these do not match, then the monitor will show the PC screen correctly, but the touchscreen will not work. Very cool design decision.

If you don't guess correctly the first time (because there are no instructions that mention this), you will spend several hours on the phone with Dell, who will then decide to ship you an entirely new monitor, you'll wait a month, try to set up the new monitor, talk to Dell again, and then finally Dell will explain how to do this correctly. With luck, and this post, you can skip these time-consuming steps.