Capacitors, fluid models, and pumps
Charge will move from a higher potential (voltage) to a lower potential. In the fluid analogy, fluid current moves from a high pressure to a lower pressure. In the same fluid analogy, charge is equivalent to a volume of fluid and a small volume of fluid can be at a higher pressure than a larger volume.

In electrical terms, Q = CV, where Q is charge, C is capacitance and V is voltage. So a small capacitor charged to a high voltage could hold less charge than a high value capacitor charged to a lower voltage. Connecting the two together would result in a current flowing from the small capacitor (with less charge) to the large capacitor (with more charge).

As to whether the capacitance can change dynamically, well yes if the area of the capacitor's plates or the distance between the plates changes or potentially, (no pun intended) if the dielectric constant of the material between the plates changes.