I have been transferring camcorder videos from VHS to digital using an RCA cable to USB adapter and when I started I encountered this same problem of the bars across the screen and weird colours/black and white output when simply recording the screen in OBS. I have a VHS/DVD combo machine and discovered, by accident really, how to overcome this and record near original quality videos on OBS. My machine does dubbing from VHS to DVD and when I did this, the problems of colours and bars were gone! I use DVD-RW discs to record to, but DVD-R ones work, too, although you can only record once to these. The rewritable discs work better when doing many VHS conversions. I hope this trick may help some of you.