An adaptable fuel cell system includes a stack generating electric energy through an electrochemical reaction between hydrogen and oxygen and applying the electric energy to a load. A reformer reforms a fuel to generate the hydrogen supplied to the stack. A fuel supply unit supplies the fuel to the reformer. An oxygen supply unit supplies the oxygen to the stack. A first buffer unit electrically coupled to the load applies an auxiliary power to the load based on usage electric energy of the load. A second buffer unit coupled to the reformer and the stack adjusts the hydrogen supplied from the reformer to the stack based on the usage electric energy of the load. In one embodiment, a centralized control unit detects a reference electric energy of the stack and the usage electric energy of the load and controls the buffer units based on the usage electric energy.