The AVT-8710 on-line manual has conflicting information; it states 15 volts DC in one place, and 12 volts DC about 5 lines down the same page. It does not list a current rating.
In any case, be sure to get the polarity correct. (Many 12 volt adapters are center positive.)
Some adapters are center positive, some may be center negative the way I read the above pose..
May be try call, e-mail, or live chat with AVToolbox to be sure.
They might even sell one for a nominal charge.
http://www.avtoolbox.com/avt8710.shtml