ESP8266 - should Vin pin supply 5V?
This link - says specifically that Vin get a direct 5V from USB's DC


Yes, it does say that. However it shows only one type of NodeMCU board. Not all NodeMCU boards are exactly the same.

I believe that your "problem" NodeMCU board is slightly different than the "working" version which is shown on that web page.



Looking at photos of the "problem" board from your supplier's link, I noticed this part of the PCB is different than the "working board". See the 2 diodes in the red ring:


(Image source - Vendor "ModuleFans" on AliExpress)

I suspect these 2 diodes are forming a Diode-OR for the two possible 5V inputs - the USB port and the Vin pin. This will prevent backpowering whichever of those two power supply sources is not used.

That means you cannot use Vin pin as a power output on that version of the board.



The photos of the "working" board are a little smaller, but in the equivalent part of this PCB, I think I see only 1 diode in the red ring:


(Image source - Losant Blog)

This is probably only protecting the USB Vbus pin from being backpowered, if power is being supplied via Vin.

If my hypothesis is correct, then that board would allow  power out to the Vin pin, when power is supplied via USB.



You would need to find and compare the schematics of the two boards (or reverse-engineer that part of the two boards yourself) to be completely sure. However my hypothesis, and seeing the different components on those two boards, support and explain the test results you have seen.