Optiplex 390 Tech Guide  Your 265w PSU won't have any trouble powering a 75w card.  I suggest the GTX 1050 over the ti version.  With the GTX 1050 ti, your CPU will bottleneck it some.  Your CPU is already the max within specs for the 390. I've relied on the YouTube videos myself.  Many of Dell's printed specs back to the time of mfr. for the generation your 390 is dictate certain model sizes with certain PSU's can't power 75w cards.  However, when specs. are successfully exceeded, Dell doesn't update.  Probably to many manuals and tech guides to reprint, though there's the internet.  Dell's 240w-290w PSU's have been successfully powering 75w cards according to many YouTubers for years. 8GB is the max listed RAM for 390.  If that can be exceeded, I'll let you research.  Something like "390 16GB ram" in Dell Community search bar.  Or check Google, ebay, newegg, to see if any are sold with 16GB RAM.  The generation your 390 is from has a habit of exceeding RAM specs. Screengrabs below: [IMAGE] [IMAGE] [IMAGE] GT 1030 is 30w.  You might have to check your games' requirements.  Naturally, the 1050 is better than the 1030. When checking bottleneck, I let the default go to 1080p.  If you run a different resolution, you can always check or have me check.
So i have an old optiplex 390 which is: i5 2400  4 gb ram  And the same psu and motherboard of the optiplex 390, motherboard is 0M5DCD and am not sure about it. My question is can i put a gpu like gtx 1650 ? Because i saw many people on YouTube using the same pc i have and they used this gtx 1650 and it works good ? Some vids used gtx 1050ti, and if they works do i need to change the power supply? And what about ram can i have 16 gb ram ? Note: Mine is the big case one 
Optiplex 390