The alternators are 28V DC 60 Amp, that would seem to be enough.
In normal flight with everything turning and burning the load is app. 10 amps each.
When you cycle the gear this increases to about 28 amps each, therefore the gear motor draws about 30 amps.
The bus voltage drops from 28.5V to about 28.3V upon moving the gear lever.
The way I understand it; the ECU's are sensitive to a voltage drop over the bus.
With a low battery ( not sufficiently charged after a GPU start) that voltage drop could cause the ECU's to shut down, apparently what happened here.
I would have to check the maintenance manual to see how the GPU plug is wired, I have a suspicion that it bypasses the battery and the pilots in question simply did not allow enough time to charge the battery, even with both engines running on the ground.
Diamond says that retracting the gear placed a load on the electrical supply from the engine-driven alternators that caused a temporary voltage drop that could not be covered by the flat battery, and the accident has shown the engine control unit to be intolerant of transient electrical fluctuations
Diamond dismisses these claims and argues the control unit supplied by TAE should have been able to accept a 50 millisecond transient, but it started to reset after 1.7 milliseconds, and during the engine control unit reset the propeller system sensed the power loss and auto-feathered.
BTW, the gear does not automatically come down with an electrical failure, over time it will slowly sag as the electric hydraulic pump is no longer able to keep the pressure @ 1600PSI. This could take a very long time though.
Here is the next scenario;
Dual alternator failure in flight, if you shut down half the G1000 system and all the exterior lights you have app. 45 min to find an airport since the ECU's need battery power to run the engines. In sight of the airport it would not be wise to lower the gear using the normal system. Considering the above mentioned article that could apparently lead to instantaneous dual engine shut down and feather. Trick would be to use the emergency extension (free fall) Need to check the POH to see if that is mentioned.
Plastic fantastic seems to have an Achilles heel, no different from other aircraft then.........