I have been using a GME PSA 1210 13.8 volt, 11 amp, regulated power supply for probably 6-7 years now without any dramas whatsoever, run all my 12 volt stuff off this unit.
My Gemini has never missed a beat, never suffered from stalls or motor lags.
I have 2 units, the 11 amp one is for my field work and I have a smaller 5 amp one for the observatory.
http://www.gme.net.au/products/acces....8v-dc/PSA1210
Cheers