$ADUser = 'me'
$ADPassword = 'Pass'
$ADPassword  = $ADPassword | ConvertTo-SecureString -AsPlainText -Force
$ADCred = New-Object System.Management.Automation.PSCredential -ArgumentList $ADUser, $ADPassword

Add-Computer -Credential $ADCred -DomainName mydom.local -NewName testing
Restart-Computer -force