You most likely don't see a difference because the phone has already plenty of charge. There is a charging curve, the phone will charge at 45 watts (~9.000mA) from 0-20%, then bring the wattage down to 37 watts until around 45%. From 45% to 60% it will charge at 30-35 watts, and above than it will be close and below 25 watts. So above 60% there's no difference when charging with a 45w or a 25w charger. A current of 4.600mA that it has shown is around 23 watts of charging power. Unless you charge your phone in quick burst, you won't need a 45w charger if you already have the 25w one. Though it will get you faster times from 0%-40% (in about 17 minutes) as the 25w charger would need around 25 minutes. Finally, if you try and see the current input while the phone is charging below 20% and you see a number of 8.000+ mA, you will notice it drop every now and then for a few seconds. That's normal. That's how Samsung manages the heat when charging at 45w.
