These chinese PSU are built for 6 GPUs, and not 12.
It mentions having 12 PCIE cables for GPUs with 8+6 power connectors. But in reality, they are meant for 6 GPUs usage.

Do not connect the motherboard's SATA/Molex sockets that are near the PCIE slots if you are going to power the risers directly, and I do not recommend using powering the risers from the motherboard at all; with 12 PCIE slots, that means you can have upto 900W going through the motherboard, which is alot.
Always power the risers directly from the PSU using SATA or 6pin PCIE.

The risers can consume upto 75W of Power (though its rare you will reach that point), but powering 3 risers using 1 PCIE/SATA/Molex rail can melt your cables or blow the fuse or in the case of chinese PSUs, the whole PSU will not work (I use these chinese ones as well.. very cheap).
It happened several times with me; I had EVGA modular PSUs, 3 risers on one rail; some of the cables melted and I had to replace them, but that was during the dual mining era.. doubt it will ever happen if you are single mining, the whole GPU barely consumes 110W.