Switching power supply feedback
High efficiency switching power have a constant volts*amps draw for a given demand. Another way to look at is is that the impedance is proportional to voltage. That's quite a problem if you're pushing the main power line near the limit. As the load increases, the voltage droops more, and the power supplies draw more current to maintain a constant power. Once the impedance of the power supplies is less than the impedance of the source, the voltage shoots towards zero. All of those switching power supplies will hit their undervoltage lock-out and turn off. The line voltage now recovers rapidly and overshoots. The power supplies turn back on and the on-off cycle continues. In small circuits, this makes an annoying buzzing sound and stuff gets hot. In massive arrays of circuits, things go BOOM.
Surely the NSA can find solutions in their "metadata" archive.