@LLG, the ‘battery bypass’ was a highly requested feature during the campaign. The projector uses up power supply itself first. Only surplus power is used to charge the battery. So if you plug in a 38W power supply, it’s barely enough to run the projector at all (need around 45-55W in normal mode), it won’t be able to charge the battery.
You may be able to charge it slowly if you plug in while the projector is off.
Also note that the power bank must be USB-C PD as @wernerj said. Power banks that only have USB-A ports will not work, they can’t supply enough power.