Details of the scenario you tried and the problem that is occurring:
Suggest we add a read-only property IsActive to the resource PowerPlan, and set that to $plan.isActive instead of setting the $Name to $null in Get-TargetResource if the plan is not the active plan.

https://github.com/PowerShell/ComputerManagementDsc/blob/c0a60754c2ec537f1668e4a3cf6ca7423a8c9a2c/Modules/ComputerManagementDsc/DSCResources/MSFT_PowerPlan/MSFT_PowerPlan.psm1#L67-L76

The DSC configuration that is using the resource (as detailed as possible):
Any configuration that hasn't the power plan as the active power plan.

Version of the Operating System and PowerShell the DSC Target Node is running:
n/a

Version of the DSC module you're using, or 'dev' if you're using current dev branch:
Dev