No worries.
I just tried out that Sega 1602-18 power supply, along with a polarity reverse plug adaptor, with my Turbo Duo.
At no load, it supplies around 14 V. So I guess this could be an unregulated power supply.
With my Duo as a load, there's still 11 V measured on the fuse, when I switch the console on.
Still, all readings in the console after the voltage regulators are fine.
The voltage regulators are getting hotter to touch than when I use my lab power supply set at regulated 10 V. The 7805 voltage regulators will accept input voltages from 7 V to 25 V DC. So I guess there's more power to dissipate into heat with higher input voltages, since - another guess - their efficiency drops with higher input voltages.
If somebody more tech-savy could tell me if my assumptions are right or wrong, please let us know.
EDIT: I'll measure the current draw tonight.