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The Samsung 25W USB-C Fast Charging Wall Charger is advertised as being able to provide 25 watts (12 volts @ 2.1 amps) to the  Galaxy Note 7 on its box. Naturally, one would think that the Galaxy Note 8 should also be able to support 25W of charging from the  Samsung 25W USB-C Fast Charging Wall Charger.

The Samsung Galaxy Note 8 uses Samsung's own Adaptive Fast Charging (AFC) technology to work with either Samsung's supplied 15W  Adaptive Fast Charging Charger or the 25 watts based Samsung 25W USB-C Fast Charging Wall Charger.

The Samsung 25W USB-C Fast Charging Wall Charger offers 25 watts (12 volts @ 2.1 amps), 15 watts (9 volts @ 1.67 amps), or 10 watts (5 volts @ 2 amps) through Samsung's AFC technology to quickly charge Samsung phones and tablets that support AFC. To see how fast this 25W charger fills up a completely drained battery on the Samsung Galaxy Note 8, we connect both the charger and phone directly using the USB Type-A to USB Type-C cable that is supplied with charger.  

Based on the Granite River Labs GRL-USB-PD-A1 power analyzer, we can see it takes approximately 2 hours and 24 minutes to charge the Samsung Galaxy Note 8 to near full from a fully depleted battery using the Samsung 25W USB-C Fast Charging Wall Charger. 

In the first few seconds upon plugin from zero charge, the phone begins pulling to about 1.5 amps current with the voltage starting at 5 volts while the phone is switched off. As the voltage goes up to about 8.8 volts, current is pulled between 1.3-1.7 amps. After 50 seconds, the phone is 3% charged and turned on during which it briefly stops pulling current while the voltage drops to 5 volts. Charging then picks up to reach around 15.1 watts (8.9 volts @ 1.7 amps) but after 80 seconds, the current drops down to near 1 amps.

In the next 40 minutes, we can see the power gradually drops down to around 2.6 watts (8.8 volts @ 0.3 amps) in between bouncing voltage and current.

When reaching about 94 minutes, the voltage and current continue to fluctuate with never a stable charging where the highest power is drawn at around 15.1 watts (8.9 volts @ 1.7 amps).   

As the Samsung Galaxy Note 8's battery nearly fills up, charging doesn't seem to stabilize as the current decreases to below 0.5 amps.

We can see that when inactive, the phone draws much more stable power to quickly charge for the first 80 seconds. When the phone is being used, both the voltage and current changes based on whether the phone is being used.

We were disappointed that we could only get at most 15 watts from the Samsung 25W USB-C Fast Charging Wall Charger to charge the Samsung Galaxy Note 8. Unfortunately, many users will purchase the premium price of the Samsung 25W USB-C Fast Charging Wall Charger assuming that it will charge the Galaxy Note 8 or some other Galaxy device faster. Perhaps due to the Galaxy Note 7 being discontinued to its fire and safety concern issues, and the fact that the Galaxy Note 7 was the only phone that supported 25W of charging, Samsung may have decided to be more conservative with the Galaxy Note 8 with regarding to how much max power is consumed using AFC technology.