Missing capacitor

I am new to arduino, and loving it. Loving lots of colored flashing lights.

Loving the 16x4 scrolling display with all the things I have to remember, scrolling by.

So now I have a MEGA and one of the two big capacitors by the 9 volt input
( I THINK that is what they are ),

but anyhow, one of them is gone.

And I can still flash a few lights.

So it is tempting to just go on and use it.

Or may be I can replace it.

So I am new to this and would like to know what someone thinks.

And I have a joke......

If a tree falls in the forest and there is no one there to hear,
does it make a sound ?

If there is no one there to hear, there is no forest.