My motherboard, an ASUS ROG Maximus XIII Apex, comes with a 6-pin PCIe power header, labelled
The spec sheet shows the following in relation to this header:
1 x 24-pin Main Power connector
2 x 8-pin +12V Power connectors
1 x 6-pin PCIe Graphics Card connector
So I assume that this is the relevant header. My GPU, which I have installed in the PCIe x16 slot, has its own PCIe power headers and works fine with those attached.
My question now is, why does this header exist? What purpose does it serve?