Can you provide the make and model of your power supply?
Aside from that, your CPU is on the budget side and will hinder the performance of high-end video cards.
Assuming your power supply is of quality, I would suggest an AMD RX 570.
The RTX 2060 is right around the corner, better than a 1070Ti, and is being introduced at $350 MSRP for the Founder's Edition.
I would not buy a GTX 1070 right now.
We need to know what you have before recommending anything.
Please list out your...
CPU:
Motherboard:
RAM:
Graphics Card:
Power Supply:
Hard Drive:
Operating System: