My installed Plex Media Server allows me to stream any local video/movie from my PC to my supported device(PlayStation 3 on my case).
When I open the Plex server on the PC, I can stream online movies & channels on the PC with no issue. I was wondering if I could use the server from the PC to stream those online contents on the PS3? I was told that Plex only support PS4.
Not sure I get your question.
The Plex player app on your PS3 should be able to play the content from your Plex Media Server.
That being said… from what I remember, Plex only actively supports the PS4. So there’s no guarantee all features will work on the PS3 as they do on other clients.