Solved meanwhile by installing some chipset recommended updates manually from the assist website  
My Drobo 5C (USB-C storage device) works fine on my Windows 10 Lenovo desktop. However, when plugged into my brand new XPS 8940 in one of the highspeed USB ports, the transfer speed is so low that it cannot run any media files. I also have a Drobo 2nd gen (old) and that one does not have any problem.  I've changed the cables, tried every USB port on the XPS 8940, uninstalled the device and reinstalled it. Drobo has checked the 5C and diagnostics say it is fine. It still runs smooth on the Lenovo desktop. Dell says, it must be a Drobo problem. Microsoft says it must be either a Dell thing or a Drobo thing. You get my drift folks. Not sure if it matters but when I look in the Device Manager under the disk drives, this is listed as Drobo 5C, the drives on my Drobo 2nd gen are all listed as TRUSTED mass storage device.  Hope y'all can make sense of this.
XPS 8940, Drobo 5C, slow transfer speed