I think I found the answer, in two ways.
I got my hands on the actual power supply, and confirmed the pin out.
Also, the plug is Hosiden TCP8927-53, Kycon KPP-3P, as found in Wikipedia's DC_Connector.
You can find the pin out in
http://www.bematech.com/support/downloads/power_connector_and_cable_specifications.pdf
I confirmed that the pin out in above matches with the actual power supply, so I am good to go.
I can probably get the Kycon KPPX-3P from Mouser, and a 16V power supply, which I plan to use a laptop power supply I can get cheap.
-- Tai