A few hundred megawatts is well within the amount of power peaker plants can produce and the vast majority are idle >> 90% of the time. You'd need millions of a

A few hundred megawatts is well within the amount of power peaker plants can produce and the vast majority are idle >> 90% of the time. You'd need millions of air conditioners to cause a brownout. Most states fine utilities heavily for any disruption of service (to the tune of $10s or 100s of millions per company per incident) in exchange for a govt granted monopoly so they all have extensive capacity built out, capable of providing for huge extended spikes in consumption.