As you can see in the image, the Dex screen hooked up to my S8+ is distorted. But the same adapter works perfectly with my dad's S9+ (image on the right).
The USB C to VGA adapter I used was this one:
I tried another adapter and this one won't even detect my phone at all. It doesn't even work when I plug it into my Tv (I have another cheap USB C to HDMI adapter from China which perfectly casts my S8+'s Dex to both my Tv's):
^I don't know if it works with an S9+ but I tested it with my brother's Macbook Pro and it perfectly mirrored the laptop screen to the LCD monitor.
Anyway, both those adapters are going back and I'm tried of buying these adapters only to return them. Can anyone recommend me a product that they already use with their S8+ and they know for a fact that it works?