Review this Apple T/N to ID your systems need: Find the right power adapter and cable for your Mac notebook

Ideally, order your charger from Apple or from an authorized reseller. There are a lot of bogus chargers which will hurt you and your system. Here's the Apple web site: MacBook power adapters

Here's a useful reference on giving your MagSafe & system the needed TLC: Apple Portables: Troubleshooting MagSafe adapters

Hopefully, these will sway you on why you don't want a fake charger:

• Lacking safety features, cheap MacBook chargers create big sparks
• Counterfeit Macbook charger teardown: convincing outside but dangerous inside