My understanding is that he is using a stellarmate pro to run his setup, and the stellarmate requires a power supply of 12V@10A (120W) for it to be able to do everything it says on the box.
I would not be looking at re-using the lighting transformer to power your mount, as mention it is designed for a very static load, and you're likely to experience some voltage collapse everytime you slew you mount.
While a bit of an expensive option, i use a
Victron Blue smart Battery charger to power my mounts. They have a power supply mode where you can set a static voltage output upto 14vdc.
They also have short circuit detection where they will not output power if it detects a short circuit on the output.