Spent some time with a Dell support tech who diagnosed the problem to be a known issue with Windowe 10. He upgraded my BIOS and driver set related with networking.  The fix has stabilized my wifi connection on the 2.5 GHz network. This is a marked improvement.   The signal strength is still lower than other devices, but at least I can use my machine now. 
works fine when close to new TrendNet AC1900, one of the more robust routers.  Take the PC to my second floor office and wifi is unusable.  Bounces on and off several times a minute on both 2.5 and 5 GHz.  changed the channel, the power mode, the aggressive roaming and updated the driver. What is my next step?  Obviously this is a significant problem and needs resolution soon. 
XPS 13 wifi another problem