Capacity of a capacitor fully charged vs half charged
While practically there are a lot of differences between a 100V and a 10V capacitor (dialectic, size etc....) 

An ideal (i.e., overlooking specifics of the dialectic differences and tolerance differences) 100V 10uF capacitor charged to 10V stores exactly the same amount of charge as a 10V 10uF capacitor.

Sure the 100V capacitor has the capability to store more (\$\frac{1}{2}CV^2\$ &amp; \$Q=CV\$) but for that operating point the same charge exists in both.