The FastCharge 2.0 standard has these charging specifications in the exact same charger (a VoltCraft car charger):
- 5 V up to 2.0 A (10 W max.)
- 7 V up to 2.5 A (17.5 W max.)
- 9 V up to 2.0 A (18 W max.)
- 12 V up to 1.5 A (18 W max.)
So the 7 V, 9 V and 12 V modes deliver pretty much the same power. The phone automatically adjusts to the supplied voltage. Some smartphones such as UlePhone Armor2 support 9V2A and 12V×1.5A.
For cables with higher resistance (i.e. long cables), the phone can 'request an increase of power' from the charger to compensate for the increased cable losses. So it's, "I want 1.66A, please increase the voltage until 1.66A is reached, I will deal with resistance control".
My question is:
When is utilizing 7 V × 2.5 A, when 9 V × 2 A and when 12 V × 1.5 A more suitable? The latter two deliver the same Wattage.