I obviously cannot speak MBB but only for the DHLC Assessment Center.
Our cases are all based on real project situations and cannot be solved by applying a generic framework. You need to carefully listen to the instructions, ask the right questions, always calculate something on paper and come to the right conclusion together with the interviewer.
You can find some training cases from DHLC on Preplounge – based on former real interview cases.
Let me know if this helps.