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The Huawei P10 phone should be able to enjoy the fastest charging with its own Huawei SuperCharge charger accessory using Huawei's proprietary SuperCharge technology over USB Type-C. While the Huawei SuperCharge charger can supply up to 22.5 watts (4.5 volts @ 5 amps or 5 volts @ 4.5 amps), it must be connected with the Huawei SuperCharge USB Type-C to USB Type-A cable to the Huawei P10. Note the Huawei SuperCharge  charger and USB Type-C to USB Type-A cable have their USB Type-A ports colored purple to help distinguish it from other normal USB Type-A ports.

Let's see how much power the Huawei SuperCharge charger actually delivers to the Huawei P10 through the Huawei SuperCharge cable over the  entire charging duration. Once the cable is attached to the charger, the charger initially shows VBUS rising up to 5 volts with no current flowing. This is unlike USB Power Delivery transactions which don't turn on VBUS until a USB Power Delivery power contract is established.

From the GRL-USB-PD-A1 software by Granite River Labs, we observe that it takes approximately 2 hours and 6 minutes for the phone to almost charge fully with the charger.

Here we can see that at zero charge, the phone starts to briefly draw around 19.8 watts (4.5 volts @ 4.4 amps) which then decreases to stay at mostly around 15.3 watts (4.5 volts @ 3.4 amps) when the phone is off or in sleep mode. When the phone is turned on and active, the current drops to reduce temperature, resulting in power charging of 5.8 watts (4.5 volts @ 1.3 amps).

In the next 62 minutes of charging, we see the voltage goes up to around 5.2 volts while the current pulled gradually decreases down to a 0.2-0.4 amps band.

When nearing the end of charging, the current mostly remains at about 0.2 amps at 5.2 volts.

Overall throughout charging, the Huawei SuperCharge charger is not providing 22.5W to the Huawei P10 as we initially expect. Even when using the SuperCharge cable, the charger only briefly delivers >15W at the starting point, but after which the power mostly stays within 15W, which is a lot lower than 22.5 watts, when the phone is off or asleep. 

We can observe similar 15W charging when using certain other USB Power Delivery chargers like the iVoler 75W USB Type C Charger as shown in this review. The Huawei SuperCharge charger is more expensive when purchased in the Huawei retail store than a lot of USB Power Delivery chargers out there, so it's disappointing that Huawei doesn't allow for even faster charging for the Huawei P10 especially given its advertising 22.5W.