The power charger charges a Kindle Fire in a short time (I just know mine is charged in a couple of hours). The standard one takes much longer (I use that when charging overnight). I don't use the power charger on my ereaders, just my Fires. In the past, using a charger rated higher than the standard for the ereader caused the battery to get warm. Not knowing much about batteries, I presume a warm battery isn't going to last as long.
I ALSO use original equipment for safety. The cheap chargers are cheap and poorly made and unless you break cords all the time (such as reading while it's plugged in and bending the connection) a waste of money. Original cords typically last the life of the item unless you roll over them with your chair.
I know, I know, many of you will disagree with me, and you are free to do so. My late brother took apart a bunch of chargers once and showed me why the cheap ones are different from the more expensive ones and it's scary that there aren't more fires (actually there are a lot of fires if you ask the Fire Dept.). There's a youtube video by some guy that shows this as well.