I have a Dell Precision T3610 workstation that currently has two 3.5" SATA HDDs installed, and I'd like to add two more 2.5" disks in a hot-swap bay. I have two free SATA ports, but I'm struggling to find a way to provide power for the additional drives.
The only spare power connector on the PSU is an 8-pin PCIe block designed to provide power for a second graphics card. The machine has a 685W power supply - my intuition is that if the PSU is designed to provide enough power for a second graphics card then it should probably be able to handle a couple of extra 2.5" HDDs (which would should only draw about 3-4W apiece) but I admit that I have not done all of the math to confirm this.
I've come across various SATA-to-PCIe power adaptors (e.g. this), but so far I haven't found the converse (i.e. male PCIe to female SATA). I suspect that there is a good reason for this - my understanding is that PCIe power connectors provide ground and +12V pins, whereas SATA also requires a +5V pin (and possibly +3.3V as well for old drives). Can anyone confirm whether my suspicions are correct, and it is impossible to power a SATA drive from a PCIe connector?
Another possibility I'm considering is whether I can use a couple of y-adaptors to split the power supply to my two existing 3.5" HDDs in order to provide power for the two additional drives. Does this sound like a reasonable approach to try?