Our final design goal is to keep the voltage variation range between the two points AB very small, no matter how the load transient current changes between the two points AB, this requirement is equivalent to that the impedance Z of the power system should be low enough. We achieve this by decoupling capacitors, so from an equivalent point of view, it can be said that decoupling capacitors reduce the impedance of the power system. On the other hand, from the point of view of circuit principle, the same conclusion can be obtained. Capacitors have low impedance characteristics for AC signals, so adding capacitors does actually reduce the AC impedance of the power system (1/jwc).