I should have read the comments before my purchase as there is a known issue with this product.
The 737 comes up with a UVP Under Voltage Protection error and it seems this is caused because the 737 does not fully support 12 Volt devices in Power Delivery mode (USB-C uses a range of voltages to keep the current down).
I did contact their support but all I got was an automated reply and as they know of the issue I would have thought their robot AI would have handled my query better.
Via the USB-A the DJI Mini 3 Pro Two-way Charging Hub charges at a very slow speed even for USB-A.
I did do a battery capacity test of the 737 and on a USB-A load of 2 amps at 5 Volts I got 73.625 Watt Hours.
Not fit for purpose so I guess if no fix is on the horizon (which I doubt) it will have to be returned.
Got am email from their customer support which confirms the issue.
Please know that our engineers have done a lot of tests on the DJI Mini 3 Pro before. And Here are our findings.
1. DJI's Charging hub states that it supports power input 5V==3A, 9V==3A, and 12V==3A, but our power bank cannot support 12V==3A. So the DJI charging hub will negotiate the power input with our power bank's C port at 9V.
2. But when we connect the DJI charging hub to our power bank, we find that the hub only asks for 9V==2A at the first, so our power bank only gives 9V==2A. That's why you will find the real output hovers around 18W. But sometimes the hub doesn't comply with the agreement, he asked for 9V=2A first but then compulsively drew 3A from our device, thus the voltage our device can finally give will be lower than 9V (because the total needs our power bank received at the very first is 9V/2A=18W, if 3A is drawn, then theoretically the final voltage will be 18W/3A=6V). Therefore, the UVP Low voltage warning will appear.
3. We also test the charging hub with some of our 9V/3A chargers (who also do not support 12V), and the testing results are also the same. So it seems that the charging hub's charging ability at 9V=3A has some unknown problems. Regarding this point, maybe you can also try some 9V/3A chargers (that do not support 12V) to see whether you can get the same results as ours, or you can also have a further discussion with DJ later.
4. We find that the charging hub's charging ability at 12V performs well. When it is charged with a 12V charger or power bank, there will be no charging issues. Therefore, our engineer will improve our power bank and add the charging ability at 12V in the near future, which should help to be better compatible with the DJI Mini 3 Pro.
5. This problem does not happen to the USB A port.
Considering the above situation, if the device cannot meet your needs and you want a return and refund, we can respect your choice.