Its a proprietary charger, like the OnePlus. I think you need the original.
I am using a Huawei Honor 8 charger and cord and it shows fast charge on the Mate 9 the same as it does on the Honor 8. If you use the charger and cord that comes with the Mate 9 it shows supercharge. I don't see much difference in charge time.
The s7 quick charger only shows regular charging, the pixel charger shows fast charging and the Huawei one says super charging. This leads me to think that Huawei will only support fast charging on the USB c power delivery standard since that's what the pixel charger is.