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Simply by attaching the Xiaomi MiBook Charger to the USB Type-C port of your Samsung Galaxy S8 with a USB Type-C to Type-C cable, both of which support USB Power Delivery technology, we'll see how well the Samsung phone's battery is topped up by the Xiaomi charger that came with the Mi Notebook Air 13.3".

The Xiaomi MiBook Charger starts charging the Samsung Galaxy S8 on a fully drained battery by offering a single 10 watts (5 volts @ 2 amps) power profile over USB Power Delivery. 

The Samsung Galaxy S8 is observed to request 10 watts (5 volts @ 2 amps) which is accepted by the charger.

Later we also observe that the Xiaomi MiBook Charger adds on four other power profiles of 18 watts (9 volts @ 2 amps), 24 watts (12 volts @ 2 amps), 45 watts (15 volts @ 3 amps), and 65 watts (20 volts @ 3.25 amps) on top of the initial 10 watts (5 volts @ 2 amps).

The Samsung Galaxy S8 follows up to again establish the same 10 watts (5 volts @ 2 amps) power contract with the charger.

After a while, we can also see the Samsung Galaxy S8 requesting 18 watts (9 volts @ 2 amps) from the Xiaomi MiBook Charger which it also complies.

However, the actual current pulled by the Samsung Galaxy S8 from the Xiaomi MiBook Charger is closer to about 1.5 amps from a fully depleted battery before it eventually settles at 1.2 amps. It also takes nearly 10 seconds for the charger to finally charge the phone at around 10.8 watts (9 volts @ 1.2 amps).