guys its called a pico psu which accepts only 12v which is supplied by the server psu, pico powers both mobo and a hdd/sdd.
ive got 2 full rigs of 6 gpus each with this setup, its nice and clean less wires going all over the place etc, soon to be 3 rigs
I use hp 1200w and 1500w platinum rated server psu's and yes its safe and secure, these psu's are little better and there made for enviroments such as we are using them in, they will last much longer than then atx psu counterparts, downside is these mostly all run on 220v only to get the full wattage