Hi

Yes, I was thinking about this and went to check the detail in the Gekodrive STEP MOTOR BASICS GUIDE, This is a extract from Section 6: Power Supplies

The easiest factor in choosing a power supply is its current rating, which is based on your motor
ratings. A motor control will always draw less than 2/3 of the motor’s rated current when it is parallel
(or half-winding) connected and 1/3 of the motor’s rated current when it is series (or full-winding)
connected. That is to say, a 6 amp per phase motor will require a 4 amp power supply when wired in
parallel and a 2 amp power supply when wired in series. If multiple motors and drives are used, add the
current requirements of each to arrive at the total power supply current rating.

With that in mind it looks like my original estimate of Approx 16 amp would be correct.