When you use multiple power supplys then you have current from one 12V rail to another because the rails are not exact the same voltage on both psu. If you power riser and GPU from different PSU then in the worst case this generates heat at the wrong place because of the differential voltage and the short-circuit current. You can measure this with a multimeter connected to the different 12V rails.

This multi PSU setups could be safe, they are probably safe if properly distributed.

SATA to PCIE 6 Pin adapter have another problem. Fake chinese wires and no proper clamping in the SATA connector... They claim to be AWG18 but they are thin as f... I only use PCIE to 4 Pin Molex and test one adapter of each bulk order by destroying it and checking the diameter of the wire.