RE: XPS 15 9550 - TPM has "disappeared"
It took me a couple of goes reflashing BiOS the first time it threw an error but the second time it went through. I think I also had Bitlocker Protection Paused when I did it. I've since found an (obscure) Dell page that tells you you have to Pause Bitlocker any time you upgrade BIOS. God knows why their utility doesn't do this for you automatically when updating!