I realize that you want to know the consequences of turning off the pc while updating Windows 10. I will try to help you with this issue.

The security update updates a DLL that is loaded in one or more processes that are required by Windows. If the computer is restarted abruptly then the DLL file is not updated. Some core system files and settings would not be updated if the PC restarts in between and as a result of this some files might be broken, damaged, or corrupt.

Restarting/shutting down in the middle of an update installation may cause serious damage to the PC.

If the PC shuts down due to power failure then wait for some time and then restart the computer to try installing those updates one more time.