Hello Michael,
I understand any of both can be used, as they fit as well a Mephisto I, so despite being an early Meph II yours is not as early as a Meph I...
The difference with the higher voltage is it is AC (alternative), so the actual voltage once internally regulated in the device is lower.
I own a Meph II (DH4005 S/N 0109560) powered by still another type of adapter:
H+G Type: DH4100
prim.: 220 V/50 Hz
sek.: 9 V/200 mA
I tested, it delivers AC.
With AC you don't need to bother about polarity at the connector plug.
With DC (should you use a generic adapter), beware (Plus inside, according to the WiKi)
MfG
Eric