Get all Columns of List (including Hidden) using powershell

Add-PsSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue -WarningAction SilentlyContinue | Out-Null

$url = "SiteUrl/"
$listName = "Listname"
$path ="C:\Temp\Columns.csv"

$web = Get-SPWeb $url
$list = $web.Lists.TryGetList($listName)
$list.ContentTypes | % { $_.FieldLinks } | select Name |  Export-Csv -path $path