On the FW16 AMD 7840HS, I have:
sudo ectool chargestate param 2
interfaces:0xffffffff
comm_init_dev being used /dev/cros_ec
7680 (0x1e00) # chg_input_current
I.e. 7680mA.
On the FW16, the 36V or 48V from the power adapter is stepped down to 20V, so the 7680mA is at 20V, so == 153.6W while a 180W FW charger is plugged in.
240W / 20V = 12000mA
200W / 20V = 10000mA
85% = 204W / 20V = 10200mA
The EC code fixes it at about 85% of the power adapter.
On the FW13, there is no step down to 20V. The FW13 tries to get 20V from the power adapter if the power adapter can do it, otherwise is boosts the power adapter up to 20V.
So, a FW13 60W PSU might be 60W / 20V = 3000mA
100W PSU might be 100W / 20V = 5000mA
100W * 85% = 85W / 20 V = 4250mA
100W * 90% = 90W / 20 V = 4500mA
The EC sets it lower than the 100% because the charger input current detection is not well calibrated, thus leaving space for calibration errors.
To properly calibrate it, one would need to somehow get the CPU to draw a constant current and then compare the EC measured value with an external calibrated PSU.