sAmaccountName by UPN in active directory
samaccountname by userprincipalname
================================
$users = Get-Content -Path 'C:\Temp\UPN.txt'
foreach ($user in $users)
{
Get-ADUser -filter * -Properties userprincipalname,samaccountname | Where-Object {$_.userprincipalname -like "$user"} | Select-Object userprincipalname,samaccountname | export-csv C:\temp\UPNOutput.csv -Append
}