You should install BIOS updates entirely outside Windows, using the F12 Flash Update option, which is less likely to fail and generally safer...

For whatever reasons, Dell removed both XPS 8930 BIOS 1.1.29 and 1.1.30 from the Support page. The last one being offered now is BIOS 1.1.28.

If 1.1.29 is working correctly for you, just stick with it, until this gets sorted out.

FWIW, my XPS 8930 has BIOS 1.1.30 installed with no visible problems, but that doesn't mean there aren't any "hidden" issues users don't see.

@RoHe​   The update for 1.1.30 is back, but still won't install - BSOD in amifldrv64.sys.  
The update is an EXE file.  How do you get the BIOS image out of an exe file?

Save the BIOS 1.1.30 .exe file on an empty (non-bootable) 2- or 4- (or maybe 8-) GB USB2 stick that's formatted FAT32.

Plug the USB into PC with power fully off. Power on and tap F12 when you see the Dell screen to open the menu. Select the Flash Update option. When that opens, use the tab key to move to the right middle box. The  BIOS file name should be visible in that box. Highlight it and press Enter. The file name should now appear in left middle box.

Confirm old and new BIOS info in top left and top right boxes. Then tab to the start button and press it.  Leave PC entirely alone until it's back at the desktop. It will reboot several times and may look like it's not doing anything. Just leave it alone until you're at the desktop.