That's the discontinued Cooler Master GX-Lite 600W. The OEM is ATNG. It does suffer from its group regulated circuit design where the +5V or +12V rail will go out of ATX12V specs when the PSU is crossloaded.
It has two 150-Watt (6+2)-pin PCI Express supplementary power connectors so it'll handle whichever ASUS R9 280X model you get.