It's been reported that Sapphire has rebranded the Radeo HD 5550 to Radeon HD 6390 in the Russian market:
The Radeon HD 6300, at least the HD 6350, HD 6370 are reserved for an upcoming GPU codenamed "Caicos", its AMD reference board even made it through a casual photo-session. The HD 5550 and HD 6390 were found to have the same device IDs. An older version of GPU Caps Viewer detects it as HD 5550, while the latest version sees it as HD 6390. The HD 5550 is based on the 40 nm "Redwood" GPU, it has 320 out of 400 stream processors enabled, and a 128-bit wide memory interface to typically connect to GDDR3 memory. Some premium models also feature GDDR5 memory.