Plot V(NOCAP) and V(DECOUP). Both rails feed the same 20 mA to 200 mA load step through 0.8 Ohm and 1 uH distribution impedance. The local 100 uF capacitor supplies low-frequency transient current while 100 nF supplies the fast edge; ESR controls damping. This is why decoupling is an impedance-versus-frequency design, not simply a rule to add one capacitor.
