I think you could benefit from reading up on retrorgb.com. He lists most consoles, what their output is and how to hook them up or mod if needed. Read up on composite, s-video, component and RGB and what is different between them.
To your question, tbh answers were already given but I will summarize:
Snes, genesis – can hook up to OSSC via RGB-scart cables.
Xbox, PS2, wii – can hook up to OSSC via component cables.
Nes, n64 – cannot hook up to OSSC
Xbox360, wiiU – use HDMI
Atari 2600 – cannot hook up to hardly anything except CRT, so I’d get that rgb modded anyway