Our users need more data =* Are you using the cables that shipped with the S3221QS? Yes* To what port on the XPS 8900 is the S3221QS connected? HDMI port used for previous monitor- Are you connecting to the onboard DP or HDMI out ports? If you mean am I connecting to the HDMI port on the computer, yes. - Or are you connecting to an added PCIe x16 video card? If yes, which specific added PCIe x16 video card? What ports does it have? No The problem became worse, with the blacking out becoming constant.  I contacted phone support and told them I don't want to go through a hundred troubleshooting steps on a monitor that I just took out of the box.  They are shipping a replacement - it seems clear that the monitor is defective. Parenthetically, I tried connecting my old monitor using the same cable that I used for the new monitor, and the old monitor works fine.
I purchased a Dell S3221QS monitor and received it today. I connected it to my Dell XPS 8900 - using Windows 10 Home, OS build 10945.3086. The monitor immediately began flashing black for a second or two, and initially did it quite regularly.  After a little while, they became less frequent - but they are still occurring every couple of minutes. There isn't really any kind of "rhythm" to it. Sometimes (just did it again) it will go a long while and sometimes it occurs every minute or two. It does not happen during any particular activity. It occurs when I am working within a document, while I am writing emails, when I am playing a game - pretty much anything.   I found one similar entry here and the user reported that the monitor was replaced under warranty. Hopefully it doesn't come to that, but I'm not off to a very good start. Any help is appreciated.
XPS 8900, new S3221QS blacking out