I have a SATA power cable from my PSU stick out the back of my computer. I also plugged a Y-Connector to the end of it.

When I plug one sata hard drive to it, everything works fine. When I plug two sata hard drives to it, the first one would stop. I zero it down to the fact that it is not getting enough power. How do I know? I took the second sata hard drive and plugged it to another external power source and both worked.

So, why is this happening? Is it the Y-Connector or is it the PSU not having enough power to the sata cable?