As you may have noticed, Simscape contains many physical domains out of the box in the Foundation Library, such as mechanical, thermal, magnetic, hydraulic, and also electrical. With a more specific license, such as Simscape Electrical, you gain access to an additional library of blocks in the electrical world, such as IGBTs, motors, transformers, etc. These electrical blocks, sometimes interface with other domains in the Foundation Library. An asynchronous motor for example, interfaces with the electrical and mechanical domain. An IGBT, can be enabled to interface with the electrical and thermal domain. The interaction between domains is easy and straight-forward in Simscape.
On the other hand, we have the library 'Specialized Power Systems' inside Simscape Electrical. This is a separate, confined domain available within Simscape to model certain electrical systems. It does NOT interact with the other domains in Simscape and gives you significant limitations. However, certain components may be modeled more extensively in this domain opposed to the other blocks in the Simscape Electrical library.
As far as I know, the 'Specialized Power Systems' library was available earlier than the other electrical blocks, and is kind of a legacy library. It is still available for people who have simulation models in this domain, or for people who do not need interaction with other Simscape domains.
I would strongly recommend to reside to blocks other than 'Specialized Power Systems'. I am even unsure if this library is still under maintenance and development (MathWorks staff may have the answer on this).
