Heya, not sure how busy Coops is today, but 500w should be perfectly fine for that system as long as it's a decently rated PSU for efficiency. Your power draw should be somewhere towards the 400w range.
It would mean that if in the future you wanted to add much more else it may be best to upgrade. It's also best just to double check your current PSU has the right connections for the 1070 you're looking to purchase
If it was me personally, I'd use it as a nice excuse to grab myself a new PSU to future proof me against any trouble my impulse buying my lead me to