If it's your psu I think the only way to check it is with a multimeter (haven't found a reliable program on-line but I could be wrong). If the power is fluctuation great enough it could be giving enough juice one moment and then dropping to not enough later.
I think we need a bit more information at this point. I looked up MacBook Pro and the new ones look like they can but without your specs I really can't say one way or another.