What is the difference between plain potassium pills and potassium gluconate pills?
In practicality, none. It is fairly simple chemistry. Potassim
(K) typically does not just exist naturally as itself. It is
usually is bonded with some other elements or substance. In the
case of Potassium Pills, it is bonded with chloride and you get
KCl. Potassium Gluconate just uses a a gluconate molecule instead
of a Cl to bind it to.
You may compare this to Na Cl or Sodium Chloride (Table Salt).
You never eat sodium alone, it is always in combination with
Chloride.
The reason in short is that when Potassium is combined with
another chemical it becomes charged positive (K+) and this is
useful for your body. Any supplement you buy that contains
Potassium, whether it be Potassium Gluconate or Potassium Chloride,
are most often the same.