Since the Atomi Power Tower Plus offers Qualcomm Quick Charge 3.0 based charging over one of its USB Type-A ports, it can be used to power various Qualcomm Quick Charge 3.0 enabled phones including the Mi 6 by Xiaomi. In addition to Qualcomm Quick Charge, the Mi 6 also supports USB Power Delivery 3.0 fast charging technology through USB Type-C, which could mean the phone may actually support the Qualcomm Quick Charge 4+.
Here we see how well the Mi 6 gets power supplied over Qualcomm Quick Charge from the USB Type-A port on the Atomi Power Tower Plus, while the phone is 2% charged and switched on. When connected using a USB Type-A to Type-C cable, the phone appears to trickle charge at about 5.2 volts in the first 20 seconds as seen through the Granite River Labs GRL-USB-PD-A1 test software. The voltage and current then increase to eventually settle out for charging to happen at around 16.3 watts (6.5 volts @ 2.5 amps).
It's good to see that the Atomi Power Tower Plus is able to deliver the Mi 6 near to the maximum 18W charging as offered by the phone's own original Qualcomm Quick Charge 3.0 based charger accessory.