In this paper we revise and simplify the notion of observationally induced algebra introduced by Simpson and Schroeder for the purpose of modelling computational effects in the particular case where the ambient category is given by classical domain theory. As examples of the general framework we consider the various powerdomains. For the particular case of the Plotkin powerdomain the general recipe leads to a somewhat unexpected result which, however, makes sense from a Computer Science perspective. We analyze this "deviation" and show how to reobtain the original Plotkin powerdomain by imposing further conditions previously considered by R.~Heckmann and J.~Goubault-Larrecq.