RedFire281

^^Agreed. Of course, I do not know your specific setup but I infer that you're using a multi-port charger. If so, you need to look at the total amp output because the ports are wired in parallel. In your case the volts are secondary because it is a 12V charger and is probably in good working order. In a multi-port charger, basic electricity theory tells us this: Voltages are the same across all components connected in parallel AND Current (measured in Amps) gets distributed over components connected in parallel. Thus, while the volts will be the same across the two ports, the total amps will be split between the two.

In order to save myself from paraphrasing here's a quote from an article I archived but don't remember who the author is: "In light of that and of the high-power demands of beefy modern smartphones and tablets there is no reason at all to buy a wimpy USB car charger. At the minimum you should always purchase a device that can provide at least 2.1 amps per USB port on the device. Simply divide the listed amps on the device by the number of ports and skip over any device that can’t meet or beat 2.1 amps. A two port device with a 2.4 amp rating? No deal. A skimpy 1.2 amps per port might have cut it a few years ago, but good luck keeping your iPhone topped off and running the GPS with that kind of weak output. Worse yet, many new devices won’t even charge properly (or at all) without 2 amps or more pouring in."

Here's an example of a good, low profile, two port charger:
Note this charger is 4.8 amps total which means 2.4 amps per port.

I hope this helps.