There are a lot of chargers out there that claim to be OEM, and even look 99.9% identical to OEM, but are not.
As said above, read reviews carefully.
Some re-pros are fine, and some are junk.
One thing you'll want to look at is how well they charge compared to a real OEM charger (charging current)
I bought a couple "claimed OEM" chargers from Newegg for $12.99.
They are not OEM but they are good copies, and the charging current is identical to the OEM charger, so that was good enough for me!