You should always install BIOS updates entirely outside Windows which is safer... Download the BIOS 1.1.28 .exe file from the Support page and save it on an empty (non-bootable)  2-GB USB stick (FAT32-formatted). Then do a normal shutdown in Windows (not a Restart). With the 2-GB USB connected, power PC on and tap F12 to open the menu. Select the Flash Update option. When that opens, use the Tab key to navigate to middle box on right side. (You shouldn't have to change any of the other boxes.) Highlight the 1.1.28 .exe file listed in that box and press Enter. Now tab to the Start button. Confirm the current and new BIOS info is correct in top left and right boxes and then launch the update. PC will reboot itself several times and may even look like it shut off completely and isn't doing anything. Just leave it alone until it's safely back at the desktop. Then repeat the process with the BIOS 1.1.30 .exe file on that USB stick. (You can skip BIOS 1.1.29.) NOTE: Some users have gone directly from BIOS 1.1.26 to 1.1.30 without any obvious problems, even though both 1.1.29 and 1.1.30 say installing 1.1.28 is a prerequisite. Up to you to decide whether you want to install 1.1.28 first or skip directly from 1.1.26 to 1.1.30.
So, I'm running 1.1.26 bios, and every installation since then has failed thru Support Assist. Dell's support assist now says my drivers are all up to date. But we know that several bios updates exists and are marked critical. I see I am suppose to go to 1.1.28 before going on up to 1.1.30. But when the exe file is downloaded, it won't install either. What to do?
XPS 8930, Bios update fail 1.1.26 to to 1.1.28