12. The capacity of a set refers to the sum of its elements. Then the total capacity of all non-empty sets $A$ that satisfy the condition “ $A \subseteq\{1,2, \cdots, 7\}$, and if $a \in A$ then $8-a \in A$ ” is
(Answer with a specific number).


12.224.

First, find the single-element and two-element sets that satisfy the conditions:
$$
A_{1}=\{4\}, A_{2}=\{1,7\}, A_{3}=\{2,6\}, A_{4}=\{3,5\} .
$$

Then, any combination of elements from these four sets also meets the requirements.

Therefore, the total sum of elements in all sets $A$ that satisfy the conditions is
$$
(4+8+8+8) \times 2^{3}=224 \text {. }
$$