That Seasonic 650W is plenty big - even with considerable overclocking or while full system stress testing, it will still leave nearly 100W to spare. So NO WAY will it be running near 100% or wide open.
and stay in the best part of the efficiency curve (50-60% load).
When a worry, it is only a worry with cheap, basic supplies that don't comply with 80 PLUS standards. But that is not a problem here. The OP has the Seasonic FOCUS Plus. That is "Gold" certified so it only has a 3% deviation from 20% load all the way up to 100% load. And being "Gold" it is extremely efficient across that range anyway at 87 - 90% efficiency!
As long as you have good cooling in your case, you can push a quality PSU near capacity all day long. And you will never be doing that.
Remember, it is extremely rare for both the GPU and CPU to be maxed out at the exact same point in time. And those are the big power hogs in our computers. But even when maxed, you won't come near 500W. That CPU is rated at a
very efficient 65W TDP. That graphics card is hungry but it still tops out at
just 250W. And unless you are running a stress test program, these devices rarely stay near capacity for extended periods of time.
If you currently had some no-name, budget generic power supply, I would recommend a new 650W quality PSU. But that Seasonic is a great PSU to start and is plenty big for your needs. Don't waste your money on anything bigger. 750W is overkill. 850W is way overkill.
BTW, I used 2 x 8GB for your RAM, 4 x 140mm case fans (even though that case only comes with 1 x 120mm and 1 x 140mm), and even added some more wiggle room for capacitor aging.
You might want to update your specs to show how much RAM you have installed and the configuration (for example, 2 x 8GB or 4 x 4GB, etc.).