Well, if anyone ever finds this with the same question here's the one I bought - https://www.amazon.com/gp/product/B00RMYWGWC (UVC Usb2.0 Video Capture Card - EasyCAP)

It worked out of the box with Linux & OBS. Can do real-time streaming no problem. It doesn't have S-video, but the video & audio quality is decent enough. I'm using it to stream older consoles like snes, n64, gamecube, etc and it works great for that. This is really the only RCA capture card I could find that stated explicitly that it would work for Linux. Despite a lot of negative reviews on Amazon, I took the gamble and it works & I'm happy with it.