One day, I took a close look at the dual power and interface cable that I'd been using at home. And I found that the adapter was different! Instead of just a steel ring at the end, the power adapter on the dual cable has an additional rubber washer. Could this be a redesign to make it fit better and stop it from shorting out the cigarette lighter socket?
Anyway, I've been using the dual cable in my car for two weeks already and the fuse hasn't blown yet so I hope this is the solution to the problem.
Since I no longer had a dual cable for use at home, I decided to order another one at Amazon. I have to wonder though how Amazon makes any money at all. It's the same item as the one I bought in October but the price is now $7 lower. In addition, they're paying for the shipping because of the ongoing super saver free shipping promo. And on top of that, I bought it through my own Amazon Affiliate link so I'll be getting 5% of that back. Their wholesale cost on the cable has got to be pretty low.