I am planning a build for my girlfriend, I am planning to get a Dell OptiPlex (390 DT Intel Core i5-2600 3.4GHz, 8GB DDR3, 500GB HDD) and add a GTX 750ti card to it, it will mostly be used for photoshop and Netflix and light gaming such as CSGO. I have noticed that the GTX 750ti needs a 6pin connector but the PSU (600w) I prepurchased doesn't have a 6pin but it does have 2 spare Molex cables, Would it be safe for me to buy a dual Molex to single 6pin to power the 750ti. If it is safe can someone direct me towards a good safe, dual Molex to 6pin as she is very limited on tech knowledge and I won't be there all the time to fix stuff if it goes wrong.
Thanks
(Edit: After some response off other forums i have been informed that there are 750ti models that do not require 6 pin, So a point in the right direction with that would also be apricated)