A 650W PSU for a 500W load is fine, but remember that PSU efficiency is highest at around 50% load.
True... but to what end? You are aware how flat the efficiency curve is, right? At most, the difference between tiers is 3%. The difference between running at 50% load vs. 66% is likely ~1%. I emplor you to take the time and do the math to see if you will ever make up the difference monetarily over the life of the PSU. I know at my 10 cents /KW /hr, I would need to F@H (24/7/365) for several years to make up the difference between the same model 650W vs 750W. And there is room to upgrade (though we're already talking flagship CPU and high-end GPU).
A 650W PSU will certainly do the job for the warranty period but it'll run hotter and louder and is less likely to last as long past the warranty period. The biggest thing that degrades PSU components is heat, and the best way to keep a PSU cool is to operate well below its peak load and in its most efficient operation range.
Just not worth it (to me).......Running 500W load on a 650W PSU is "well below its peak load" and still quite close to "its most efficient operating range". For 80+ Gold, the MAXIMUM difference allowed between 50-100% load is 3%...
That advice only serves to spend more money for no/little tangible reasons. Buying a PSU to run it at 50% load is a monumental waste of cash. 60-75% is a great sweetspot between price, headroom, and quiet operations.
EDIT: I just ran a game (Forza 4) with a 'CPU' @ 5.2 GHz 10c/20t with a stock RTX 2070... want to know what the kill-a-watt said? I peaked at 301W (at the wall) during the benchmark.
EDIT2: The Division 2 - 362W peak (ran around 325W).
EDIT3: AIDA64 stress test... 290W.
EDIT4: A64 stress test + Furmark, 460W.
Again, all values are at the wall, so take away 10% for efficiency.
So, I stand firmly behind the 650W will be plenty fine. Truth be told, 550W would be too...though 80% is pushing things a bit for quiet operations (depends on the unit and what you have in your case). Id also run a 2080Ti on a 650W PSU without a bit of worry. Doesn't get much more than that.....