Power problems with Raspberry Pi model 3B+ and Allo Boss DAC v1.2

Hi,
I have encountered an issue when trying to power the Raspberry Pi model 3B+ from the Allo Boss DAC v1.2, i.e. attaching the power cable to the USB C socket on the Allo Boss board and powering the Raspberry Pi through the GPIO. I use ethernet cable and wifi/bluetooth disabled.
The Allo Boss‘ onboard power regulator seems not to be able to deliver the necessary power to the Raspberry Pi 3B+.

I am using a linear power supply that delivers 5.2V (5A) to the Allo Boss DAC. However, on the GPIO, I measure about 4.6V (which is too low). The power consumption is around 600 mA at startup, falling to around 500 mA in „idle“.

The low voltage to the Raspberry Pi makes it „unreliable“, i.e. sometimes the Raspberry Pi does not finish the startup process, because the voltage is too low, which is also confirmed on the monitor with „Under-voltage detection“.
I have tried with two Raspberry Pi model 3B+s; the issue is the same.

If I use an „old“ Raspberry Pi model 3B in the same setup, there is no problem – and the sound is wonderful.
The voltage on the GPIO is a little more than 5V (5.05V) and the power consumption 250-300 mA.

Unless any of you have another explanation, my deduction is that the Allo Boss v1.2s onboard regulator/filter is not designed powerful enough to power the Raspberry Pi model 3B+ via the onboard USB-C connector.

I would like to hear, if anybody else has experienced the same issues.

Have a nice day,
Anders