Agree, my S5 charges at 1.2A given a charger capable of this, and that is fast.
correction S5 chargers are shipped with a 2.0A chargers and it charges at that rate.
Yes I think in the end it is something around this current. What the apps report is more "charging in 1800mA mode" and not really charging with continous/real 1800mA. If you like to know more exactly what the current is you may write down time/percentage values for e.g. every 5% of battery power starting with an nearly empty battery. Then you can draw an line of the effective loading current.While it's true that the phone ships with a 2A charger, the charging current does not exceed 1.2A AFAIK.
correction S5 chargers are shipped with a 2.0A chargers and it charges at that rate.