I have brought an amplifier from mini-circuits. It has one terminal for supply of +12 V. I guess, I should connect the center-pin of this terminal to positive DC supply(red) and ground (black) to the end of the terminal as shown in the figure below. Is this correct?

 

Your photograph is a little blurred!

Have you got a link to the actual amplifier.

 

yes,
https://www.minicircuits.com/WebStore/dashboard.html?model=ZHL-6A-S+

 

Yes, except that it needs 24V (but not exceeding 24.5V).