With two computers failing on two different inputs and with multiple power sources it certainly seemed to be something with the monitor. I disconnected all cables from both computers and the monitor. I held the power button to discharge circuits in the monitor. I re-ran the cables very carefully in an attempt to minimize contact between the power cable and the video cables (see comment below). The Aurora R11 video (DP-DP) hasn't flickered since. The Latitude 7400 2-in-1 (HDMI-HDMI) has only flickered a couple of times. The HDMI connector is closer to the power connector so there is a bit more chance of EMI. I've ordered a new HDMI cable and will see if that completely eliminates the problem. I haven't had a ton of time on the computer this week but I did test refresh rates with the R11 up to 100Hz and no flickering. I'll call this one fixed, at least for now. Comment: I would like to point out a design flaw in the location of the power connector in relation to the video connectors on the AW3420DW. The power cable must run in close proximity to the video cables since it's farthest out on the monitor and the connectors are all side by side. Depending on how the cables are run through the stand and into the monitor, the distance of close proximity is probably 12-18 inches. It would be better to have power on one side of the stand and video on the other.
My AW3420DW has flickered since day1 but seems to be getting worse. The flickering is not consistent although it seems to happen more right after start-up. Sometimes it flickers every couple seconds and then there are long periods where it won't flicker at all. I've connected it to two different computers (Dell Latitude 7400 2-in-1 and Alienware Aurora R11 w/ GeForce RTX 2080Ti) using both HDMI and DP. I've tried moving the power cord from the UPS to the wall. Same results with all combinations.  The Latitude runs at 3440x1440 / 50Hz. The R11 normally runs at 3440x1440 / 60Hz. I've also tried 50Hz and it still flickered. I tried 85Hz and the problem is so bad I have to wait for the settings to revert.  Note: when it flickers the power button changes back to white like the monitor is going to sleep. Thoughts?
AW3420DW, flickers on and off