Can I power via the header?

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Hi guys,

I have Up Core Plus and Vision Plus X.
I'm developing custom hat board.
I will have a configuration where 3 of them are connected to each other.

My custom board will have 12V power supply.
I'd prefer to power both Up Core Plus and Vision Plus X via the 100-pin header rather than power jack.
My question is is it safe to do so?

Thanks,
Miks.

PS
Also, can you please point to the specs page for Vision Plus X.
The main page for the device only has BUY button.
I can only see one photo of the device.
I cannot even tell if it has headers on the other side or if it has a heatsink.