I should have added the PSU info I guess then
Orange PI 4, v1.3 board
model 4 (non NPU), no eMMC, booting straight from SD
PSU: 5V 3A (official RPi 4 USB-C PSU) and 5V 4.5A (official Thinkpad X1 Carbon USB-C PSU)
tested with downloadable Armbian_20.02.0-rc1_Orangepi4_buster_current_5.4.14_desktop.img (2020-01-25)
tested with manual build using current code base in GitHub (master branch), with Buster + 5.4.y kernel, server, standard
As the board is working with a build from Xunlong, I don't think the PSU is the problem here - even if I would love the solution to be that easy.
And for the time being, I can't help much as I'm still expecting to receive a new UART dongle...