Hello, this is my first post here!
Those capacitors are in series, so the circuit sees 1 capacitor with double voltage (200V+200V=400V) and half the total capacitance.
As a rule of thumb this total capacitance is approximately the maximum wattage the psu can do, as long as the psu is not ACTIVE PFC.
680uF: 300-350W max (depending on the psu design)
820uF: ~400W max
1000uF: 450-500W max
1200uF: 500-600W max
560uF: 300W max if the psu is well designed
470uF: 250W, maybe 300W peak for some seconds
Please pay attention, many capacitor manufacturers lie about the capacitance of those caps. Especially Deer/L&C/Premier/Allied/Force etc uses caps labeled 470uF for example, but their real C measured is 330uF!
If you replace 680uF with 820uF the only bad thing that would happen is that the inrush current will increase and that might stress the NTC input current thermistor. But I have done it many times in the past without any problem.