Definitely not for Alex Kidd like that.
Hmm. Does Alex Kidd use a progressive video mode? If that is the case, the jitter is definitely not normal.
@wumbo64, what does the LCD on the OSSC say when you play Alex Kidd? What is the voltage level of the sync signal when using your cables? If it’s 5V TTL, then you should modify your cables to lower the voltage level to avoid wear on the components of the OSSC.