John -
Congratulations. It sounds like you have been a great dad/granddad and solved the problem twice over. You did something nice and small and convenient without spending a pile of cash. Also, kids kind of hate AC transformers because they don't understand why they are forbidden to ever turn the enticing big knob on the transformer. Good luck.
I have to imagine, based on the video and common sense, that Lionel designed Lionchief to work on a variety of widely available power supplies. They do give you guidance, but the voltage is not critical.
Worst case scenario - even if your high voltage power solution does eventually burn out their locomotive, it seems like it will take a good long while.
Also, I would just reiterate to anyone reading that you can't really compare volts AC to volts DC. It's an apple to oranges comparison between two very different animals - for a variety of reasons.
