Sometimes we need working with PowerShell objects which have attributes with hyphens. That can be a bit difficult as PowerShell assumes hyphens are used with operators and parameters.
Below is an example on how to get around this, and rename the attribute:
$Users = Get-AdUser -Filter * -Property "msDS-ResultantPSO" | Select name, @{Name="ResultantPSO";Expression={$_."msDS-ResultantPSO"}}