$buses = get-wmiobject -class "Win32_Bus" -namespace "root\CIMV2" -computername "."
foreach ($bus in $buses) {
   if ($bus.BusType -eq 5) {
      $mos = (new-object System.Management.ManagementObjectSearcher)
      $mos.Query="Associators of {Win32_Bus.DeviceID='" + $bus.DeviceId + "'} WHERE AssocClass = Win32_DeviceBus"
      $mos.get() | foreach {$_.caption}
   }
}