What did it break by charging MacBook Pro with a repaired MegaSafe?

Sounds like you got a bad MagSafe charger.

There are quite a few clones out there which can damage your system! I'm suspecting the one you bought was one of these. Here's more on why you shouldn't buy these: Counterfeit Macbook charger teardown: convincing outside but dangerous inside and take a look at this: Lacking safety features, cheap MacBook chargers create big sparks

Here's a good Apple T/N on checking for a damaged unit and to check your computers MagSafe port: Apple Portables: Troubleshooting MagSafe adapters

Sadly, it sounds like your system was also damaged by the bad adapter. You'll need buy a REAL MagSafe adapter to see if your system was damaged. You might also need to replace the MagSafe port if it got damaged: MacBook Pro 15" Unibody Mid 2010 MagSafe DC-In Board Replacement

If your system was damaged by the cloned adapter you'll need to sue the company that sold you the bad adapter to get damages to get your now damaged computer fixed. Now the hard part depending on where you live you might not be able to sue or the cost to sue will be more than getting your system fixed on your own.

Here's the IFIXIT guide to replace your logic board: MacBook Pro 15" Unibody Mid 2010 Logic Board Replacement and the needed part:

• MacBook Pro 15" Unibody (Mid 2010) 2.4 GHz Logic Board - Apple P/N 661-5566
• MacBook Pro 15" Unibody (Mid 2010) 2.53 GHz Logic Board - Apple P/N 661-6361
• MacBook Pro 15" Unibody (Mid 2010) 2.66 GHz Logic Board - Apple P/N 661-5480