Local Administrators list on all workstations, remote machines.

Create list of Computers with below command

Get-ADComputer -Filter * | select name > c:\computers.txt

Execute below Script: It will create c:\localusers.csv
# ==============================================================================================
# NAME: Listing Administrators and PowerUsers on remote machines

#
# COMMENT:
# This script runs against an input file of computer names , connects to each computer and gets a list of the users in the  local Administrators
#and powerusers Groups . the output can be a csv file which can be readable on excel with all the computers from the input file
# ==============================================================================================
function get-localusers {
        param(
    [Parameter(Mandatory=$true,valuefrompipeline=$true)]
    [string]$strComputer)
    begin {}
    Process {
        $adminlist =""
        $powerlist =""
        $computer = [ADSI]("WinNT://" + $strComputer + ",computer")
        $AdminGroup = $computer.psbase.children.find("Administrators")
        $powerGroup = $computer.psbase.children.find("Power Users")
        $Adminmembers= $AdminGroup.psbase.invoke("Members") | %{$_.GetType().InvokeMember("Name", 'GetProperty', $null, $_, $null)}
        $Powermembers= $PowerGroup.psbase.invoke("Members") | %{$_.GetType().InvokeMember("Name", 'GetProperty', $null, $_, $null)}
        foreach ($admin in $Adminmembers) { $adminlist = $adminlist + $admin + "," }
        foreach ($poweruser in $Powermembers) { $powerlist = $powerlist + $poweruser + "," }
        $Computer = New-Object psobject
        $computer | Add-Member noteproperty ComputerName $strComputer
        $computer | Add-Member noteproperty Administrators $adminlist
        $computer | Add-Member noteproperty PowerUsers $powerlist
        Write-Output $computer


        }
end {}
}

Get-Content c:\computers.txt | get-localusers | Export-Csv c:\localusers.csv