I've got a similar OTI VGA/EGA card - the jumpers select if the card outputs on the VGA or EGA port and most likely what type of monitor is connected to the EGA port and maybe it can be locked down to CGA modes. I'll add my experience with the card I own since I believe things will be more or less the same...
The OTI is basically a VGA with the ability to select ega output on the DB9 TTL port. I have tested mine in EGA mode and found quite a few games thinking it's a VGA and their display was either garbled or had wrong colors. In the end I just reverted to using a real EGA card.

The DB9 TTL port can't display VGA modes so 256colors on any resolution or running vga games through it is a no-go.
These cards were made during a transitional era AFAIK and they just support EGA through their VGA chipset and a connection for your old monitor so you wouldn't have to scrap it.
Speed-wise the OTI card I have is even faster than my ATI EGA WONDER 800 - but the compatibility problems just doesn't worth it.

Thanks for the detailed info! While looking in my box of spare cards I also found two other dual 15pin/9pin cards... an OTI 037C and an Orchid Peanut VGA. But I suppose none of them would have true EGA compatibility either. I guess one needs two rigs then... A 386 EGA and a 386 VGA 🤣