I know exactly what you mean regarding the PwC case interview; when I interviewed for PwC's Tech practice, one of the "cases" was literally just 1 question on how I would setup a technical backlog!
Frankly, you need to be prepared for anything (sorry). This means you should be prepared for "standard" cases AND transaction strategy & execution cases. Additionally, you need to be prepared for a classic case format (prompt, exhibits, etc.) AND brainstorming (quick prompts/questions requiring one after) AND unstructured cases (multiple questions, asked sequentially, with verbal information given but no charts/exhibits).
The key is to be flexible/adaptable here and always maintain 1) An objective-driven approach and 2) Structured + concise thinking and communication