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Charging can be done, by the way, through a USB cable attached to a USB port on your computer. I just wish to mention that in case the knowledge is useful. (Charging through a computer's USB port and a USB cable, is a bit slower than using a wall adapter, however.)
This charger for Kindle (available throug WalMart's website) :
has a longer end than others such as this perfectly standard one:
or others, much the same.
The first one, with the longer plug, is actually designed not just for the Kindle, but for other devices too - some of which may require the longer plug. So I think that explains the difference, and be assured, the shorter one is standard and is OK.