The status of the desktop reported in Admin UI is combination of ADAM data and the latest volatile state reported by Agent to Broker.

There's a no Powershell equivalent to get the states. But you can query the ADAM to get the state.

1. Check if the Agent is responsive vdmadmin -A -d desktopname -m machinename -getversion

2. Check if the VM is READY and has zero sessions (use Get-DesktopVm cmdlet)

3. Machine entry in ADAM has the pae-dirtyfornewsessions attribute set to 1 for this desktop