AMD has released OEM-specific variants of RX 500 GPUs for both desktop and mobile. Dubbed the RX 500X, this is a simple re-badging exercise for OEMs help in advertising new systems. The RX 500X series are exactly the same as their corresponding base parts but OEMs can tune their clock speeds for thermal and power reasons.
https://www.notebookcheck.net/AMD-launches-OEM-specific-Radeon-RX-500X-series-GPUs-for-desktop-and-mobile.296902.0.html