vivo is launching the X300 Ultra on Monday, and Oppo is working on its very own competitor to that device, the Find X9 Ultra. We already know that it's coming in April, and that, like the X300 Ultra, it will be available globally.Whereas vivo's Ultra has optional teleconverters taking it to high zoom levels, the Oppo Find X9 Ultra will have a built-in 10x telephoto camera. Oppo released a new teaser today calling it a built-in 'teleconverter' of sorts, clearly throwing some shade vivo's way.Oppo Find X9 Ultra 50MP 10x periscope telephoto camera detailsThe Find X9 Ultra has...