Sync Outlook 2013 with iTunes 12.5.1 Recently upgrade iPhone 6S to 10.1  and iTunes to 12.5.1  Mainly use iTunes to sync my Outlook contacts and calendar via USB cable only (not Wi-Fi).  Appears to begin sync and stops part ways through process and sounds as though sync is complete.  Do not use iCloud for sync.
In case you don't want to use iCloud, you can try 3-rd party software called AkrutoSync. Unfortunately, there's no way for syncing over USB, only via Wi-Fi or over the Internet. The best part is that this software works with iPhone's native apps which I found very convenient. Here's a link to their website: http://www.akruto.com/sync-iphone-with-outlook/

The bad thing is that you have to reconfigure this software each time you want to switch between syncing over the Internet to syncing via Wi-Fi.