After the last Windows Update (this morning), I haven't seen the high memory use yet.  I will wait a few more days to see if it is actually fixed.
Optiplex 7780 AIO, just purchased a couple days ago.  I have all window updates loaded on Windows 10 OS. I also have all recent/available Dell drivers loaded.  Desktop Window Manager goes from using about 30 MB of memory at startup to well over 3 GB (3000 MB) in just a couple of hours.  While there is still PLENTY of memory left, this situation can only be "fixed" by restarting the PC.
OptiPlex 7780 - Desktop Window Manager using way too much memory