The Xiaomi Mi 8 not only can use Qualcomm Quick Charge 4+ technology to support USB Power Delivery 3.0, PPS (Programmable Power Supply), and Qualcomm Quick Charge 3.0 based charging over USB Type-C but also charge other phones and tablets as well as being able to be charged itself. Here we observed how the Mi 8 uses its dual-role power capabilities to charge the Apple 12.9-inch iPad Pro over USB Power Delivery 2.0.
Note to use the Mi 8 as a power bank to the Apple iPad Pro's or iPhone's supporting USB Power Delivery that can only consume and not supply power, the Mi 8 will need to drain its own battery charge to support charging the Apple 12.9-inch iPad Pro so make sure there's enough battery charge on the phone.
Using the Apple USB-C to Lightning Cable, we connected the Mi 8 on a 100% full battery to a 13% charged Apple 12.9-inch iPad Pro. The Xiaomi phone will automatically charge the iPad Pro since the iPad when connected automatically just supports charging in.
Over the first 60 minutes of charging we could see the Apple 12.9-inch iPad Pro drew constant power of mostly around 7.6 watts from the Mi 8 which resulted in slow charging for the iPad given its big battery. After the battery has charged for an hour, charging consistently stopped and resumed to about 7.6 watts over repeated intervals. To view more details, click here to download the trace captured by the GRL-A1 power analyzer.
Rather than USB Power Delivery, 7.6 watts charging is more similar to the 7.5 watts USB Battery Charging 1.2 spec. While the iPad Pro can charge faster with its own Apple 12W charger, the iPad Pro can still get charged by the Mi 8 when missing the Apple charger.