I just purchased a U3818DW monitor and so far looks great, only one problem I noticed with my (not-validated by Dell) 2017 MacBook Pro. ..when connected via USB Type-C directly to the monitor, the laptop is also charged, that's great...the problem appears when I put the laptop on sleep - I get a notification popping out at about 20-30 seconds that the battery is fully (100%) charged and this notification also wakes up the monitor. Is there a way to disable this maybe from a monitor setting or Mac OS? Couldn't find anything so far. I'm on the latest firmware for the monitor.
I have the same problem with an MacBook (2017, no Air, no Pro) when connecting to a Samsung S27H850QFU screen via USB-C. Looks like an macOS issue then?!?