At the frequencies computer chips operate, it acts more like AC. Sure, you place some nice bypass capacitors capacitors very close to the chip so you can feed it nice clean DC power, but when you start switching those transistors in the GHz range, the signals inside the chip rapidly start to look a lot like AC.
You see the same thing with external signals, like a connection between CPU and memory. Operate the bus at 1MHz and it is effectively DC. The signal has a wavelength of 300 meters, so when the signal travels a distance literally two orders of magnitude smaller across your motherboard the AC behavior is negligible. Operate that same bus at 1GHz and your wavelength is down to 30cm. Got a 40cm-wide motherboard? Better treat it like a transmission line or it isn't going to work!
The latest versions of USB and PCIe are no longer binary digital signalling at all. It is a modulated radio signal [1] carried over a wire, similar to how DSL and cable modems work. Processor and memory busses will be next to switch over. Most digital systems will probably move in this direction as speeds continue to increase.
High-end CPUs are actually not powered directly by DC. Basically all server (and growing portion of consumer) CPUs are powered by multiphase buck regulators[1] which split the power from from the DC PSU rails into a parallel set of modulated buck regulator power stages. The outputs of the parallel regulators are recombined to generate DC (as the combined waveform of the phased AC parts).
The reason for this multiphase design is because it offers better power efficiency and better transient response to the CPU as the CPU moves between it's different power states (high vs low load).
Even on the DC input which ostensibly isn't doing anything it will probably be wiggling around a lot. You can attack electronic safes by analyzing the power draw into their computer as you type into
You see the same thing with external signals, like a connection between CPU and memory. Operate the bus at 1MHz and it is effectively DC. The signal has a wavelength of 300 meters, so when the signal travels a distance literally two orders of magnitude smaller across your motherboard the AC behavior is negligible. Operate that same bus at 1GHz and your wavelength is down to 30cm. Got a 40cm-wide motherboard? Better treat it like a transmission line or it isn't going to work!