The equivalent capacitance of the combination shown is

There are four capacitors each of capacitance C.

Notice the two vertical capacitors in the middle are short-circuited.

Why?

Their top plates are connected to the top wire, and bottom plates to the bottom wire — but those top and bottom wires are already directly joined together at the right side by a conducting wire.

So both vertical capacitors have zero potential difference across them:

V=0

They contribute nothing.

Only two capacitors remain:

• top-left capacitor C
• bottom-left capacitor C

Both are connected directly between the left terminal and right terminal.

So they are in parallel.

Equivalent capacitance:

$$C_{eq}=C+C$$

=2C