>>716010554
VGA out from a Radeon R9 380 (you need a supported Radeon GPU, but a lot of them work) going into pic related and then a regular SCART cable from it to the TV.
The box is just a sync converter, plus it provides some voltage level on one of the pins to tell the TV it should display the RGB input (SCART has composite and S-video on the same connector too, so this is required or you may get a black screen). This setup outputs proper 15kHz 240p/480i, it can even do those weird 55Hz or whatever the fuck modes that some arcade games use.