Decentralized stabilization and control schemes for large-scale power systems are presented in this paper. The interconnections between the subsystems are assumed to be unknown, but bounded. The control design for the first scheme utilizes the knowledge of the bounds on the interconnections between the subsystems, whereas this information is not required in the second control design due to its adaptive nature. These schemes are applied to a power system with two generators and an infinite bus connected through a network of transformers and transmission lines. Simulation studies for unknown interconnections arising due to faults and subsequent line switchings in the transmission network are carried out. The studies not only illustrate the simplicity of the developed controls, but also validate the fact that connective stability and robust performance is maintained for unknown interconnection topology using these schemes.