The only negative results I've seen reported from using a non-Kindle charger has been slow charging, and some actually draining the Kindle's battery, somehow. (Not that you couldn't have something go more wrong - just sayin, so far, I haven't seen it reported.)
If you want to play it safe (and want it to work faster than 3 days), there are chargers rated for Kindles for sale for just a few bucks on Amazon. Like $3.
I also saw one bundled with a K3 case, for around $10. You can also look under K2 accessories to find just the chargers for cheap.
