This issue is currently tracking, but those that applied the .NET update for April 2017 can no longer issue a stop-computer command (used to shutdown the computer) in PowerShell. This happens both when run as a non-administrator or using administrator credentials.
A workaround is offered here: https://superuser.com/questions/1199285/stop-computer-privilege-not-held
The issue is being investigated by Microsoft and, if this affects you, you are asked to open a support case.
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