I found this thread through Google and registered to warn anyone else who finds this thread.
Listen to everyone else and DO NOT buy a knock off charger.
I bought one off eBay when my old one kicked the bucket. The knock off lasted a few weeks before nearly catching on fire. It'd get
incredibly hot, and the plastic casing around the wires would begin to melt. Every time I plugged it in, a barrage of sparks would fly out of my outlet. After the first week, the wires would spark if they collided with each other in an unfriendly way.
And what's worse is that it completely killed my MacBook Pro's battery life. It now only lasts about an hour unplugged, as opposed to its old 3-4 hour lifespan. I don't mind since my laptop rarely leaves the house, but I'm just thankful the damage isn't worse.
The funny thing is my original charger died the day after the one-year warranty expired, and the Mac store refused to bend the rules

.