I'm having the same problem with my MacBook Pro, my U2718Q just falls asleep and won't wake up when my MBP wakes up. My second monitor, a 27 inch Acer K272HUL monitor wakes up with no problems. Sometimes unplugging and plugging back in the USB-C Cable works, sometimes I have to restart the Dell too, and occasionally reboot the MBP too. This problem seems to be getting worse. Since Dell isn't going to support Macs with this monitor, is my only choice to return it?
As I stated in the other U2718Q thread, because we never validated the Apple proprietary hardware, operating system (including Windows Bootcamp), and drivers, you should ask the Apple users on their Apple Forum for troubleshooting help. Perhaps they can recommend a specific Apple USB-C to DP cable or Apple OS settings. For my notes, send me via Private Message the service tag number.
You understand that's a recommendation to return the monitor? I'm not going to spend my time scouring forums for tips from other users, this is a $500 monitor that I specifically paid extra for so I could get higher quality and support.
I don't understand Dell's refusal to validate this monitor for use on Macs. It's a premium monitor for professional use, Macs have massive market share with professional users (Apple's average Mac unit price is close to $1,400) and MacBook Pros are the most popular professional laptop. When an old Acer monitor works better than a new Dell monitor it's a sad day.
"$500 monitor that I specifically paid extra for so I could get higher quality and support" I hear your complaint, but based on the above online documentation, there is no support for Apple OS and hardware.
"Macs have massive market share with professional users" Apple was only 9.6% of the 2017 laptop share.
Global laptop share, TrendForce, 2017 = HP 24.3% (Windows OS) Lenovo 20.2% (Windows OS) Dell 15.2% (Windows OS) Apple 9.6% (Apple OS) Asus 9.5% (Windows OS) Acer 8.0% (Windows OS) Other 13.2% (Windows OS)
"I don't understand Dell's refusal to validate this monitor for use on Macs" The data from TrendForce shows us that the U2718Q works with 90.4% of the market running a true Windows PC and operating system. It is just not cost effective for Dell to pay our monitor manufacturers more money to test on the Apple 9.6% share. Which is why an Apple user should ask the Apple users on the Apple Forum for help and advice.