充公 is a separable verb (离合词) meaning "to confiscate (by the state or authority)". The verb 充 and the object 公 can be split: you can insert 了, 过, or other elements between them, e.g. 充了公 ('confiscated'), 充过一次公 ('confiscated once'). It's used in legal and administrative contexts when the government seizes private property, assets, or illegal gains. You'll often see it in passive-style constructions with 被 or 把.