You don't want the BIOS .rcv file on the USB stick. You want the BIOS .exe file on the USB stick. Give that a try...
I have a new XPS 8950 and I see there is a new BIOS 1.4.0. I would like to install this, but I don't have Windows on the machine. So I followed the instructions for other operating system: download BIOS_IMG.rcv and copy it to a USB stick, then start BIOS Flask Update from the boot menu. The BIOS update tool sees my USB stick but doesn't offer any files. The instructions say to press the "... button" to browse the USB drive, but there is no ... button. I did reformat the USB stick first as FAT32. I see these instructions below but the 8950 flash upgrade tool does not look the same as the one in the screenshot. Flashing the BIOS from the F12 One-Time Boot Menu I currently have the 1.2.1 BIOS. Can someone please advise how I can do this upgrade? Do I need to rename the file?
XPS 8950, can't install BIOS 1.4.0 from boot menu