I have an article for you here that can help you troubleshoot this charging issue a little further. That article can be found right here:
This is an older article, but it will still walk you through the proper steps for troubleshooting the charging issue you are experiencing. Take care, and thanks for visiting the Apple Support Communities.
Many thanks for your reply.....
I did in fact have an online chat with an Apple rep.... who advised me that the 12w usb charger is NOT compatible with the ipod Classic but is ok for my ipod Shuffle. I would need the 5w usb charger for my Classic. So i have purchased the 5w charger and indeed it does work fine on the Classic. so i will be returning my 12w charger to the Apple store when next in the locality......
I really think Apple need to make this MUCH clearer on the advertising!!!!!!