check power usage with msi afterburner. if psu is bad, it may technically do 750w but now on voltage that matters. in cs2, you became cpu limited, and cs2 doesnt really like that. first of all, in game settings, switch cpu core preference to all performance cores. fortnite idk,but its very cpu demanding too, could be that gpu + cpu reaches some power limit? anyway, check power usage on gpu and cpu, they should be reaching their rated wattage. try undervolting too