Thank you for answering!
The power supply has enough current for all modules.
The voltage drop in the line, not in the power supply, because I need to use some meters of cable because of the distance among modules.
My doubt is: is it better to supply a 12V relay with a lower voltage or a 9V relay with a higher voltage?
I think the second choice is better because it can work from about 7V to 12V, but I don't know if it is dangerous to supply a 9V relay with 12V.
Thank you