If the first plates of all the capacitors connected to common terminal and second plates of all capacitor connected to common terminal and these terminals are connected to opposite terminals of battery.
Let c₁,c₂,c₃ are three capacitors connected in parallel as shown in figure

In parallel combination potential on each and every plate same. But charge varies from plate to plate. Total cahrge of the combination
$\mathrm{Q}={\mathrm{Q}}_1+{\mathrm{Q}}_2+{\mathrm{Q}}_3$
But $\mathrm{Q}=\mathrm{CV},{\mathrm{Q}}_1={\mathrm{C}}_1\mathrm{V},{\mathrm{Q}}_2={\mathrm{C}}_2\mathrm{V},{\mathrm{Q}}_3={\mathrm{C}}_3\mathrm{V}$
$\begin{array}{l}\mathrm{CV}={\mathrm{C}}_1\mathrm{V}+{\mathrm{C}}_2\mathrm{V}+{\mathrm{C}}_3\mathrm{V}\\ \mathrm{C}={\mathrm{C}}_1+{\mathrm{C}}_2+{\mathrm{C}}_3\end{array}$