NVMe power issue?

[tsys]

I've just designed a small daughterboard with a step-up/step-down regulator that might fix the issue.

Nice work Tobias.

Thanks 

It looks easy except for the part where you join the through holes on the adapter board and the daughter board. How do you ensure heat transfer through via pairs to get a solid connection?

Usually that is not really a problem. Once solder has flown into the holes thermal conductivity is pretty good and the capillary effect will just suck the solder through to the mating surface of the two boards. Worst case I'll have to put a short piece of wire through the holes before soldering them.