I did the updates as indicated by Dell with the two BIOS versions on separate USB sticks. The only hiccup occurred when I initially tried to go to the BIOS 1.1.29 update from a restart. The BIOS file selection screen seemed to look funny.  When I did a shutdown/powerup to get to the BIOS update screen the 1.1.29 update worked fine.
The update page for XPS 8930 BIOS 1.1.29 is stating that BIOS version 1.1.28 must be installed first. Do you know the reason for this?  I am currently at BIOS version 1.1.26.
XPS 8930, BIOS updates, order?