If you are taking the power depth exam, I recommend these books: Electrical Power Systems Technology and Electrical Systems Design, both by Theodore Bosela. I read both of these cover to cover and did the problems in them, probably did both of those things twice, and then used Schaum's outlines for additional practice problems, and I felt like I nailed the PM portion of the exam. (My degree is in electrical engineering (i.e. electronics and control systems) so I didn't know any of the power stuff from school.)
I started studying in February for the October exam, which was probably overkill, but I wanted to try to do 1 hour/night every day. In the beginning I probably studied like this 4x/week, and by the end I studied every day, 2 or 2.5 hours a night during the week and 4 hours each Saturday and Sunday. If you are a "typical" geeky engineer (!) you may actually kind of enjoy the studying - I did!
Good luck.
Oh, and these boards rock! Great for motivation or a little study break.