Have you ever used a power chair (the second one)? I don't know about California, but in Florida it may be more difficult to rent a power chair since they are more difficult to learn how to use. Some companies won't rent you a power chair unless you have experience using them. I would recommend an
ECV, you can try them out at your local grocery store or big box store. Much shorter learning curve.
I don't have any experience with these companies yet, I've always used Deckert Surgical in the past, but the owner retired and they're not in business any more. I'm planning to use one of the companies I listed on my next trip, so I can report back in a few months.
I chose these because they had several mentions on the Disneyland forum here, you can search by their name to find some previous mentions/experiences.