I just found this VERY similar ac adapter on Amazon.com,
Dunlop ECB-06 18V Power Adapter
This adapter is sold through Musical Instruments Vendors as it is used by a line of Guitar pedals.
It appears identical to the REB1200 ac adapter I have, and is 18Vdc and 1000mA with center positive. They don't state the od, but
similar Dunlop adapters (like ECB-003, ECB-04), do mention a similar looking plug is 5.5mm.
It does look identical to my ac adapter in every respect except the Vendor's name on top!