If you need to know whether file is, you should use "Test-Path" cmdlet in PowerShell.  It returns "True" if the file or directory exists and returns "False" in other case.

$fpath = "C:\output.xml" 

$isfile = Test-Path $fpath 
if($isfile -eq "True") {
     Write-host "File exists"
}
else {
     Write-host "File doesn’t exist"
}

There are some more good things in this cmdlet. Write "man Test-Path" in your PowerShell console and read about it.