You might not be aware that not all USB chargers are made equal. Without going into technical details, the type of charger and cable you have might significantly affect how fast your cell phone will charge. If you leave it charging overnight, it is probably not such a big issue, but if you want to quickly pump some juice during a layover in an airport it could become critical. It is not always easy to predict based on phone and charged features their compatibility, so I decided to do a quick test using P3 International P4400 Kill A Watt Electricity Usage Monitor. I tested the following equipment:
1. AT&T Samsung Galaxy S4
2. HTC One
1. iXCC (tm) Dual USB Port FAST 2.1A 10W AC White Travel Wall Charger
2. Stock USB charger which comes with Galaxy S4
4. Apple USB charger
1. Samsung USB cable (white)
3. Generic USB cable (black)
You can see pictures of raw measurements here
The conclusions are:
1. Cable does matter. Samsung cable provides fastest charging (charger permitting)
2. Galaxy S4 can draw more current than HTC.
3. Samsung and iXCC chargers performed the best (about the same except iXCC has 2 ports you can use simultaneously).