To get the current power plan..

---------------------start code---------------------------------------------
# Get the active power scheme
$activeScheme = Get-WmiObject -Namespace "root\cimv2\power" -Class Win32_PowerPlan | Where-Object { $_.IsActive -eq $true } 
# Output the active power scheme
Write-Output ("The active power plan is: " + $activeScheme.ElementName)

------------------------------end code-------------------------------------

To change the plan to Balanced..
-----------------------------start code------------------------------------
# Get the Balanced power scheme
$balancedScheme = Get-WmiObject -Namespace "root\cimv2\power" -Class Win32_PowerPlan | Where-Object { $_.ElementName -eq 'Balanced' } 
# Set the Balanced power scheme as active
Invoke-WmiMethod -Path ("ROOT\CIMv2\Power:Win32_PowerPlan.InstanceID='" + $balancedScheme.InstanceID + "'") -Name Activate 
# Output the result
Write-Output "The power plan has been changed to Balanced."

----------------------------end code---------------------------------------