I agree that if you take at once a quantity significantly greater than the recommended daily intake, for instance ten grams of potassium, there may exist some people with a combination of health problems, where instead of causing diarrhea such a dose would be absorbed in the blood instantaneously and some kidney disease will prevent the immediate elimination from the blood of that potassium, which would cause hyperkalemia.

On the other hand, if the dose does not exceed the recommended daily intake and it is taken after a meal, then it is pretty certain that it cannot have any bad effects in anyone who is not already dying.

There is absolutely no difference between the potassium contained naturally in food and the potassium added by a supplement. Therefore anyone who would be affected by the recommended daily intake would be equally affected by natural food or by a potassium supplement.

The main reason why potassium supplements are necessary is because potassium is lost very easily from food as a result of the methods used for preparation. Any kind of soaking or washing or boiling where the water is disposed is guaranteed to remove a part of the potassium (and of the magnesium), possibly most of it.