After adding C2, when the local circuit needs a momentary high current, the capacitor C2 can temporarily provide current for A. Even if the common part of the inductance exists, the voltage of the A terminal will not drop too much. The effect on B will also be much reduced. Therefore, the decoupling effect is played by the current bypass. Generally, large-capacity capacitors are mainly used for filtering, and the speed requirements are not very fast, but the capacitance value requirements are relatively large. If local circuit A refers to a chip, and the capacitors are as close as possible to the power pins of the chip.