What voltage of charger should be used for the Kindle Fire?
Is there one made specifically for the Kindle Fire?
You need to get the specific kindle charger from amazon. Using any charger could burn your circuit board and that's the end of the kindle's life. The kindle fire charger has INPUT (AC): 100-240V, 50/60Hz
OUTPUT (DC): 5V, 1.8A. I have provided the link to amazon where you can get the original replacement charger for the kindle fire.
here is the link >> www.amazon.com/gp/product/B005CKAX82/
Y trying with new charges, you might be having data cable wire which is provide by the kindle company u that cable for charging
if still you need buy IPHONE USB charge,
Yes there's one specially made for the Kindle Fire. See here, it discussed the charger, charging time, and how to optimize the battery life of the Kindle:
You can go into the official charger details page, it's 9W, 1.8A, so it's 5V.
Hope that helps.