For unknown reasons Adtran *REALLY* makes it hard to find this stuff!
Yes, it's designed to run from -48V office battery.
Connector is a Kycon KPPX-3P. Mouser has them as well as other distributors.
Installation manual here - NetVanta 4660 and 5660 Hardware Installation Guide
Manual lists pinouts for every single thing on the box except the power connector! AC power supply is part 17004661F1. If you have one and a voltmeter you can ring it out. Page 33 describes the power requirements.