To see if the data pins of my USB charges were at the wrong voltage, I used a hobby knife to open the plastic case.
The cases were glued together so I had to break open them. The Car USB chargher, though, had the top that was screwed on.
I was happy to find fuses inside the two: my iPod should be safe!
As you can see on the pictures the data pins are floating and that is why my iPod did not want to charge.
The specifications of the stickers on the items say that the wall plug can provide no more that 500 mA while the car charger no more than 1000 mA. I decided to stick to 500 mA for both of them.