This issue appears to have been resolved in BIOS version A16.
I'm having issues with Secure boot on a Power Edge T20 but only when running Windows Server 2016. I'm trying to figure out if this is a BIOS issue or a hardware issue or if anyone else is experiencing it. BIOS: A02-A12 Boot Type: UEFI with Secure Boot Enabled OS: Windows Server 2016 Standard (verified ISO) Basically what happens is the server will not reboot it only hangs before reboot. When it goes to reboot. It  sits at a black screen indefinitely. It does not get to the Dell BIOS Logo. It even gets as far as turning off USB devices like the keyboard. It will do a full shutdown though without issue. This actually happens even during OS install. The first reboot it during the install it hangs. If I turn off secure boot it works fine. If I use Windows Server 2012 R2 with secure boot enabled it works fine as well. I have tried it will all the published BIOS versions for the T20 and can reproduce it even on A12. To reproduce: Set bios to defaults. Make sure Secure boot is enabled for UEFI. Try to reboot Windows Server 2016. The Dell Poweredge T20 is certified for Windows Server 2016 as of BIOS A09.
Poweredge T20 Secure Boot with Windows Server 2016