2000mah is good for the normal Kadas Vim, for the Khadas Vim2 you need more power.
As exemple i show a good adapter.
Its the adapter for the Raspberry 3100mah 5 volt.
It haves a OTG plug, so you need a plug from OTG to USB-C. (In China 10 for 4 Dollar)
The link is to a Dutch store to show you what I mean. (15 euro/16 Dollar)
And the plug for OTG to USB-C : https://www.allekabels.nl/htc/5780/1371998/usb-micro-naar-usb-c-adapter-20.html
For the starter of this topic,
If you need good firmware, I can help you no problem.
(One thing, I have only Android, not Duall Os versions)
Send me a email : email@example.com , and i send you some files out my Dropbox.
In the beginning i haves also problems.
When i send a email, i put inside a user manuel how to use this firmware, and i give the good working software.
Sorry for my English, I speak it good, but on paper hahaha #Helppp
Normaly i Always in the Dutch forums, thats easyer for me.
When you send me a email, you have it in the end of the week.