An on-die-capacitor structure includes a first capacitor and a second capacitor. The first capacitor may have first and second terminals. The first and second terminals are directly connected to first and second power supply rail structures, respectively. The first power supply rail structure is different from the second power supply rail structure. The second capacitor may have third and fourth terminals. The second capacitor is connected in series between the second power supply rail structure and a third power supply rail structure. The third power supply rail structure is different from the first and second power supply rail structures. The third and fourth terminals are directly connected to the second and third power supply rail structures, respectively. The first capacitor may have a first capacitance and the second capacitor structure may have a second capacitance that is greater than the first capacitance.