R9 200 series doesn't tell us much. What exact card do you have?
These support FreeSync:
Radeon™ RX Vega series
Radeon™ RX 500 series
Radeon™ RX 400 series
Radeon™ R9/R7 300 series (excluding R9 370/X)
Radeon™ Pro Duo (2016 edition)
Radeon™ R9 Nano
Radeon™ R9 Fury series
Radeon™ R9/R7 200 series (excluding R9 270/X, R9 280/X )
oh i'm sorry it's an R9 270 Dual-X OC With Boost, 2 Go so it should be supported right ? i mean "excluding R9 270/X" is'nt my case because the dual-X OC, is'nt it ?
No...the 270 or the 270x is not supported.
oh well ... thank you for your help though !