If you do not mind using linq/NET, this will list users present in BOTH lists:
$file1 = import-csv -Path "C:\ps\output\adusers.csv"
$file2 = import-csv -Path "C:\ps\output\users.csv"
[linq.enumerable]::intersect( [object[]]($file1.name), [object[]]($file2.name) ) |
Export-Csv -NoTypeInformation -Path "C:\ps\result\result.csv"
Linq does not have method opposite/reverse to intersect but you can use SymmetricExceptWith from generic collections.
Code below lists users who are present either in one list or another but not in both at once:
$file1 = import-csv -Path "C:\ps\output\adusers.csv"
$file2 = import-csv -Path "C:\ps\output\users.csv"
$res = [Collections.Generic.HashSet[String]]( [string[]]($file1.name) )
$res.SymmetricExceptWith( [string[]]($file2.name) )
$res | Export-Csv -NoTypeInformation -Path "C:\ps\result\result.csv"
Note: this code may not work on earlier powershell versions.