You can use `categories and keywords` for classifying different types of content like pages of different products in your example. <br><br>So, in your example the department/electronics will be the category and TV, PC etc will be keywords. On the keywords classify the `banner components` like PC keyword will have `PC banner component` classified on the keyword. <br><br>
On save of a page in a certain structure group like "PC", automatically `classify` the appropriate keyword using the event system to the newly created page. <br><br>Create the banner components as a `dynamic components` so that you don't have to publish the pages everytime, when you change banner images in the banner components. <br><br>Now, from DD4T you will be able to get the classified keyword on each page which will have the TCM uri of the banner component. You can query for the same using TCM uri and render the same in any page by calling render dynamic component method from DD4T. This logic of getting and including the dynamic component will be on your page template (which can be c# razor view or its equivalent in Java)