Hi!
Have here a Dell Optiplex 7020 with BIOS A18 (latest). When I shut down Leap 15.2 (in GUI, with “shutdown -h now” or via “init 0”) the machine shuts down, but after 1-2 seconds it reboots again. I can press the power button, but after some 1-2 seconds it will reboot again. If a pull the plug it will stop (of course), but reboot again on plugging in again, but with pressing the power button again it will shut up, finally. Very annoying.
The BIOS option “Power Management” -> “AC Recovery” is set to “Last power state”, as the machine is sometimes used as a router/firewall.
With Win 7 or BSD I have no such problems on this machine (was comparable with Leap 15.1, but I could stop the rebooting by pressing the power button).
Any ideas how to stop this? 
I don’t have a definitive answer here, but FWIW I just wanted to share this long-running kernel bug report that may be of interest to you. Maybe worth trying one of the quirks mentioned?
Hi!
I added
xhci_hcd.quirks=270336
to the kernel parameters in YaST -> Bootloader and now the machine shut’s up eeh down correctly!
Many thanks!
PS: Wow, the initial report dates back to 2013! Nobody really cares? A problem with the USB-driver? Hmmm… forgot to say: Keybord and mouse are connected via a USB-“switch”:
https://www.aten.com/global/en/products/usb-&-thunderbolt/peripheral-switches/us424/
Glad that boot parameter did the trick. I’ve since seen a number of similar threads/discussions like this. It’s also mentioned here…
https://wiki.archlinux.org/index.php/Wake-on-LAN#Wake-up_after_shutdown