Like i find on google, 750Ti's has 6pin connection
https://thepcenthusiast.com/nvidia-geforce-gtx-750-gtx-750-ti-maxwell-graphics-card-surfaced/
so seems you need at least psu with 6x 6pin connectors to power up gpus' if they dont have it you dont need it.
Just note you cannot mine ETH with these cards, as DAG file bigger than 2gb