Much confusion exists regarding the dissectible Leyden jar Myth: When the experiment is performed high voltage electrons are indeed "sprayed" onto the surface of the glass, or any other dielectric.
While on the surface the glass, the (dielectric) undergoes molecular polarization. The "ENERGY" is stored in the "FIELD" which now consists of the "ELECTROSTATIC FIELD ENERGY" keeping the molecules of the glass polarized. The important thing to remember is that electrons themselves are not "ENERGY". The "ENERGY" now in electrostatic form still resides in the "FIELD" not in the electrons. In the case of a vacuum capacitor the "ENERGY" is still in the field, the electrons on the plates merely cause the "FIELD" to exist. Once the concept of electrostatic field energy is wrapped around your head, the myth disappears. I have performed MANY experiments to confirm what I have stated, as to not spread and misinformation regarding the concepts. I believe it is at this level of learning, that misunderstood concepts can lead to MUCH difficulty later in more involved electrical phenomena. Using a mechanical analogy: It is stated in physics books that a rock lifted and placed on a table now has "POTENTIAL" energy. The MISCONCEPTION is now the rock itself has energy, when in reality the energy exists in the "FIELD" between the rock and the ground. There is energy stored in the "rock-Field" system, and the "FIELD" is furnished by Gravity.