Are they the same because apple gives yuo the cable but you can buy the power adapter
The USB 2.0 cable supplied with the iPod can be used to charge and sync the iPod. The cable can charge and sync when connected to a computer. The power adaptor is for charging the iPod through the SAME USB CABLE which is supplied with the iPod through a normal power outlet, this is useful if your USB ports are occupied or you are travelling without your computer.
the power adapter is so you can charge it off of a regular outlet rather than having to have a computer handy to charge it through the usb port. i recommend getting the power adapter, i have it and its good