Whoops, forgot about the 3rd pin, my fault. 
The Y-cable of Amazon probably does not fit for PCIe (reviews)
How do you know that a riser needs less than 50W? I've nowhere found infos about that.
The Y-cable of Amazon probably does not fit for PCIe (reviews)
Powered risers draw less than 50 W and are perfectly safe to use with a SATA connector.
How do you know that a riser needs less than 50W? I've nowhere found infos about that.