I recently purchased a referbed Dell XPS 15 and from day one Windows Update would fail. In my case the cause was a combination of Dell setting a registry key to override the update and status server address to an internal Dell IP and apparently not having the correct Windows Firewall rules in place.
I removed the registry key and ran the FixIt app here. http://support.microsoft.com/mats/windows_update/
Note that some folks online are saying you can simply change the value UseWUServer to 0 to accomplish the same thing.
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate] "WUServer"="http://172.23.49.241" "WUStatusServer"="http://172.23.49.241" [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU] "UseWUServer"=dword:00000001