Slight change in power calculation. Maximum power draw will be around 360 W with the GTX 1070 Founders Edition video card installed.
Ah! The Rosewill Capstone 450 W PSU is a good quality unit!
Since the existing PSU has been revised to 450 W, and it is the Capstone version, then this PSU should be OK for use with the GTX 1070 video card together with the other existing hardware. So upgrading the PSU is not really necessary at this stage.