Adding RTX 2070/2080/2080TI with GTX 1080 TI

I already have a Gigabyte GTX 1080TI and a slot left wherein I’d like to add another GPU. Ideally, it would’ve been perfect if there was GTX 1080 TI available in the market but since it isn’t where I live, I was wondering if I could add RTX 2070/2080/2080 TI in the other slot.

Anybody in the forum have experience of pairing up GTX and RTX cards?

Suggestions and advises are always welcome.