uppercase,lowercase, capitalize some text

This and much more -- String Manipulation plugin.

But for simple uppercase/lowercase -- "Edit | Toggle Case" should be enough.

If I select from Edit the menu entry it works but pressing ctrl+shift+U does not work. In my case it type "u underlined" 

@Malutanpetronel

In my case it type "u underlined"

What's your primary keymap / language selected? Does not sounds like it's English (as it has no "u underlined" symbol).

For me it looks like your OS takes the priority here when dealing with keyboard input. If you go to "Settings/Preferences | Keymap", there is a button next to the local search field that allows looking for actions by assigned shortcuts -- use it and press that shortcut there -- will it find that action? If not -- well, the OS intercepted the shortcut before it goes to the app.

In such case I suggest you simply change the shortcut for that action from Ctrl+Shift+U to some another one that works for you (on that "Settings/Preferences | Keymap" screen).