Well, the OP wonders why, obviously, the PSU and the Pro1 cannot agree on any charging protocol, which is strange indeed. Depending on the power source, my Pro1 seems to distinguish between three different charging modes: "charging slowly", "charging", and "charging rapidly". The last is probably chosen only if the PSU explicitly supports Qualcomm QC.
Electrically, one of the lower two modes should always be possible. I've been charging my Pro1 with solar panels ... 😎