I need to pick up a second power adapter for my 13" MacBook Pro to keep in my bag to take with me to work. I don't particularly want to spend the $75ish for an Apple one if I can avoid it. Is there a decent cheaper 3rd party adapter out there that works well? Also, I kept my spare 85w adapter from my late 2006 15" MacBook Pro when I sold it to buy the 13". I know in the past you couldn't use higher wattage power adapters with lower wattage notebooks. Is that still true? Or can I just use my old one with my new machine?