From my understanding, Flextronics is just the manufacturer for Apple in this case.
The charger supplied with my MacBook Pro also says 'Flextronics LPS' (bought directly from Apple).
So while I cannot guarantee it's a genuine charger, the imprint 'Flextronics LPS' is definitely not suspicious in any way.
And the print/logo in your picture does not look counterfeit to me (unlike other chargers I've seen).