Add a user to a local Windows user group with PowerShell. Inspired by https://mcpmag.com/articles/2015/05/28/managing-local-groups-in-powershell.aspx

add-user-to-group.ps1

$Computer = $env:COMPUTERNAME
$GroupName = 'Topology Manager Administrators'
$ADSI = [ADSI]("WinNT://$Computer")
$Group = $ADSI.Children.Find($GroupName, 'group')
Write-Host ("Found group '{0}'" -f $Group.Name.Value)

#$User = $env:USERNAME
#$Group.Add(("WinNT://$Computer/$User"))

$User = "domain\username"
$ntUser = "WinNT://" + $User.Replace('\', '/')
$Group.Add(($ntUser))
Write-Host ("Added user '{0}' to group '{1}'" -f $User, $Group.Name.Value)

Write-Host ("'{0}' group members:" -f$Group.Name.Value)
$Group.psbase.invoke('members')  | ForEach {
    Write-Host (" {0}"-f $_.GetType().InvokeMember("Name","GetProperty",$Null,$_,$Null))
}