Strange PSU behaviour with 2 SSDs

I'm on MacPro 5.1 with GTX Titan.. Since i bought an external PSU for the Tity, i decided to use it for my SSD too..
The PSU is an OCZ ZT 750 W.. I used the paperclip trick between the 4th and 5th pin (green and black) to let it power on without mobo and it all worked great..

Then I just got my second SSD and things became absurd.
When i plug both SSD the PSU powers on and then shuts off!
What I tried to do to verify (i have 3 sata cables, each has 3 connectors)(i made this try with the Mac off, so the whole power was available):

- Plug one SSD per time (one cable, one connector). OK
- Plug one SSD on a rail and one on another (2 cables). SHUTS OFF
- Plug both SSDs on the same rail (one cable, 2 connectors). SHUTS OFF
- Changing cables and repeating these 3 points. SHUTS OFF
- Changing rails and repeating these 4 points. SHUTS OFF
- Using a Y sata splitter from a connector of one cable (one cable, one connector). SHUTS OFF

I tought one of the 2 SSDs could be faulty, but they seemed ok when put in the same working condition.
The OCZ shuts off when he has 2 SSDs connected, no matter on which cable or connector or rail.
It looks like when he has to power more than a SSDs he dies.

Faulty PSU? What do you think?