I am the person that will be helping you today.
Yes, you can purchase such an adapter for your Garmin 2689LMT.
You can purchase the AC Adapter at the following page: http://www.amazon.com/Travel-Charger-2639LMT-2689LMT-MYNETDEALS/dp/B00NUAVNV2
If you need anything else in the future, please let me know.
Thank you for your time today.