Hope it goes well. Can you compare the difficulty to any of the practice exams you took? I have all the same material so just want a gauge. I feel like Zach's test is brutal but filled with so much good info
I have not yet taken the actual PE Power exam, so I can't fully answer your question.
But I will try to rank the difficulties of the various practice exams that I took...
In my opinion, from hardest (1) to easiest.
1. Cram for Exam Volumes 1 thru 4 (80 questions each volume) - various quantitative questions of decent to hard difficulty, and also many qualitative/conceptual questions that are pretty tough. They also have a good amount of topics not covered by the NCEES handbook. I memorized and committed to memory a good amount of things I learned from these exams.
2. Electrical PE Review
3. Engineering Pro Guides (I would say Electrical PE Review and Eng Pro Guides are about the same level in difficulty, actually.)
4. PPI PE Power Exams (IMO there are some good fair-game questions of decent difficulty I think might be on the actual exam, but then also they cover more than what I would think the exam would actually have. For example, they have questions about cross vectors and determinants, which we wouldn't think would be on the actual exam.)
5. Shorebrook PE Power Exam
6. Complex Imaginary Exam Practice Book (4 practice exam sets: each set is 80 questions)
7. NCEES PE Power practice exam
8. A.S Graffeo Practice Exam (as Dothracki said above, it is rather outdated at this point... But I still use it for practice.)
9. Spin-Up PE Power Exam practice sets (many of their quantitative problems are way too easy, but I feel they do have a couple of good conceptual/qualitative problems regarding power system stability and a few other uncommon topics)
This is my opinion on the various PE Power practice exams I have used to prep up.