A system comprising a plurality of stacks and a plurality of converters, each of the plurality of converters is operable to charge a corresponding stack for adsorbing ions in a liquid, wherein when one of the plurality of stacks is charged or discharged at a first state, one of the plurality of converters associating with the stack operates in a first mode, and is configured to indirectly convert a first voltage to a second voltage at least by an intermediate stage, one of the plurality of stacks is charged or discharged at a second state, one of the plurality of converters associating with the stack operates in a second mode, and is configured to directly convert the first voltage to the second voltage.