RE: Windows 10 - WiFi does not work
After reviewing my notes, it might have been the following two driver updates that helped. These driver updates are specific to XPS 8700, but I imagine there similar updates for other Dell desktops, laptops, etc. Dell made it much easier with the System Detect tool.
Windows 10, 64-bit
Driver and description: This package provides Dell DW1704 802.11 b/g/n Driver and is supported on XPS 8700 running the following Windows Operating systems: Windows 10.
Download URL: www.dell.com/.../DriversDetails;fileid=3479174503
Release date:8/13/2015 7:54:10 AM
Driver and description: This package provides Intel 7260 WiFi Driver and is supported on XPS 8700 running the following Windows Operating systems: Windows 10.
Download URL: www.dell.com/.../DriversDetails;fileid=3475171474
Release date:7/29/2015 3:10:01 AM
I also highly recommend subscribing (via email or RSS) to Dell Technical Updates. They are almost a secret (not on purpose) as it is hard to find the "how to subscribe" info by searching the Dell website. That link will take you to the right web page though.