If you really want to charge your Kindle from your PC then buy a Palm Zire USB cable. It has two tips that split off the main cable. One is your USB small device plug and the other is a power tip that is perfect for the Kindle. I haven't used the wall charger since I bought this. And I use the USB to sync with my PC and the USB plug also will charge other devices so I leave this cable hooked up to my PC and and use it with my camera, MP3 players, Kindle, and compatible phones.
I found my cable for less than $5 shipped off of eBay. This was the single best accessory I purchased for the Kindle.