USBC-DP cable from MacBook Pro late 2016 to Dell 27U15H monitor is a no go.

Not recognized at all. Nada.

Ouch. Completely operator error. Used wrong DisplayPort on the Dell (there are two). Thank you David W. for the quick response. Product works great. Thanks!!

Glad to hear of the solution, Alan! This is a common gotcha on Dell monitors with multiple DP ports for input and output.

Posting other common DisplayPort troubleshooting steps from David’s email below for the benefit of others who may be researching similar issues:

Some quick settings to double-check, if you haven’t already, would be to make sure that the DisplayPort input is being selected as the input source and to see if disabling MST/DisplayPort 1.2 in the monitor’s menu could help ( page 41 of the manual here –>… ).