A charging current is controlled by the voltage difference between the charger output, and the battery's terminal voltage.
You should check what current is actually flowing using both charger adapters.
You could easily find the 1.25mA device is only inputting 1 mA, or the 2mA device is inputting even less than that.
Besides, 1.25mA is a ridiculously low charge rate. I think you are reading the mains current rating, not the output current.If so, there would be very little difference in output current, if output voltage were identical.