You can check on PSU label how much have Amperes can supply on 12V rail.
Example if PSU have 40A * 12V = 480W now you must check how much your entire PC drain from 12V, add power consumption CPU + GPU + 50W-100W rest PC parts + 20-25% safety margin.
And check if your PSU is ratted on Tier list best are 1,2 , 3 is for low budget , and 4 for office use ,5 avoid.