$web = Get-SPWeb http://SITE
$user=$web.AllUsers
$user|Select LoginName,@{Name='Groups';Expression={$_.Groups -join '|'}} | set-Content -Encoding UTF8 filename

or

get-SPUser -Web http://SITE|Select LoginName,@{Name='Groups';Expression={$_.Groups -join '|'}} | set-Content -Encoding UTF8 filename

or 

get-SPUser -LIMIT ALL -Web http://URL |Select LoginName,@{Name='Groups';Expression={$_.Groups -join '|'}}|select-string XXX|select-string "=}" -NotMatch |set-Content -Encoding UTF8 file.csv


#$user|Select LoginName,@{Name='Groups';Expression={$_.Groups -join '|'}}|select-string XXX|select-string "=}" -NotMatch |set-Content -Encoding UTF8 blabla.txt