hst222 was correct.
His (or her) answer wasn't merely Uninstalling of Dell software. (I had already uninstalled SupportAssist because it was intermittently running at 99%, locking up users, forcing reboots.)
aside: SupportAssist isn't named "Dell SupportAssist" in Windows GUI. It's just SupportAssist. I had removed that and left a few related Dell apps, but removing the main one had solved the CPU 99% problem, so I had left the rest of Dell helpers installed.
hst222 told me to remove DellInstrumentation from Device Manager (first, change View to By Drivers).
I didn't find that listed under D for Dell, looking in alphabetical order.
I found that under O for
oem118 DellInstrumentation.inf
(Details: Dellsupportassist)
On a different computer here, it was
oem198 DellInstrumentation.inf , so the oem number varies.
Remove that from Device Manager if you have not yet done so.