Check out Mactracker on the App Store. This free app will help you find the exact model and spec of your Mac (or iPad, iPhone, Apple TV, etc) which will make it a lot easier to figure out things like:
- how many watts power supply you need
- max RAM capacity
- graphics card capability
- speed of USB port
It turns out my mbp is “late 2008” or MacBookPro5,1, and contrary to what the Apple site and Crucial say, it has a capacity for 8GB RAM, which I think it needs.