you will need more power it will be dangerous to run it with 300w you can run it without using the power cables but I dont recommend it at all, also do you already have it because it will be bottlenecked(other components wont use it to it's full potential) because a 750 ti or even lower card would be a better choice, maybe even save up a little more for a full system build
I hope I helped just ask if you didnt understand what I said i'm here to help and i'll try my best as will everyone else.