Default Big difference in charge speed between usb car chargers

I've tested two different car chargers, charging the Galaxy S4 at low battery in the car:
  • Energizer CC15141: 460 mA
  • Cheap dual usb ipad charger: 1200 mA

The dual usb for ipad allows up to 3.1 A top one or two at the same time.
The Energizer is up to 1 A

I guess the dual usb for ipad emulates wall charger, while the energizer does not, so the difference in charge speed.
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