tiny voices :
The PSU should be changed to 500w or at minimum an XFX450w unit.
450w is the lowest you want to go with an hd7870
Not at all! That build will run just fine with a 430 W PSU. It may be cutting it a little close, but you're still fine and have a good number of watts for headroom. You may want to upgrade to something a little more just for the purposes of future proofing, but 430 W is perfectly fine.
To the OP, PC Partpicker has an accurate Wattage calculator built in. You can see it at the top right of any of your saved part lists after you click "view". It's very accurate. Who says 450 W is the lowest you want to go? At peak load, the Radeon HD 7870 consumes 170 W. It's all about the other components and how they add up. Anytime AMD or Nvidia claims that "such and such power supply is recommended" that's just bull. AMD even makes a note that wattage is dependent on all of the parts combined, not any one individual part. Hell, even a GTX Titan only consumes 260 watts.