We propose a decentralized output-feedback controller for a general class of interconnected large-scale systems. Each subsystem in the large-scale system is comprised of a triangular (strict-feedback-like) system coupled with an appended Input-to-State Stable (ISS) dynamics. The design is based on our recent results on a new adaptive high-gain control design approach utilizing a dual high-gain observer and controller architecture with a dynamic scaling. The technique provides strong robustness properties and allows the system class to contain unknown functions dependent on all states and involving unknown parameters (with no magnitude bounds required). Both the uncertain parameters and the appended dynamics are allowed to be coupled with the entire system state.