Try this:

https://www.tenforums.com/windows-updates-activation/109012-1803-issue-hybrid-laptop-discrete-gpu-connected-display-3.html

" had the same issue. I have an Alienware 15 R3. Failing with the same error as all of you at 49%.
But... my husband also has the same model and his update went through fine.

So it led me to wonder why?! the answer - He took "all the Alienware junk" off his and I hadn't!!

So I uninstalled Alienware update and digital delivery utility and just left Alienware command centre and Alienware onscreen display installed.

I also uninstalled the latest Nvidia driver, put my laptop into airplane mode and restarted. I let Nvidia put its basic driver back on and waited for everything else to load on my system (leaving airplane mode on). I don't personally feel this step is necessary, but if the above fails for you, then you can try it.

I then re-ran the windows update and it worked!!

So, personally I don't feel this is a microsoft fail, I think the common denominator of all the people with problems is Alienware, and those of us who have that Alienware update and digital delivery installed. "

Do not go around the block:

https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install/hybrid-laptops-with-discrete-gpu-connected-to/3518f6b4-c267-4d38-b5b9-d5ea0c16e975?tm=1525314302049&auth=1

Side effects include not being able to wake from sleep.  Go Back to 1709 under Settings > Update & security > Recovery