Hi to all!
I've just passed PSPO 1 (95%), Honestly: the exam is not very difficult but there are too many really "confusing" questions, so read very carefully. Also you have to understand that there are enough questions which are not in Scrum Guide.
Resources to pass PSPO1 (in my mind):
1 - Scrum Guide (surprise :) )
2 - Volkerdon.com - again (as in PSM) very good resource. In my mind (this is not advertisement) - very and very helpful. Maybe you will not agree with me, but I've passed this exam also by their help.