The possibility of a phase transition to proceed reversibility within an electrified interface is examined. It is shown that the inhomogeneity of a real interface and in particular the existence of a diffuse layer is likely to put serious obstacles for a phase transition to take place reversibly, especially when the controlled electrical variable is the electrode potential. However, their occurrence cannot be ruled out. Reversible phase transitions may be more easily observed if the electrode charge density is used as the independent electrical variable. Irreversible transitions are also expected under charge density controlled conditions. In this case negative capacities might be observed. Finally, the various problems about the clarification of the nature of a phase transition experimentally and the implications to their theoretical description are also discussed.