[jacquesm]

The easier way to achieve that goal is to overload the net rails with a few thousand volts after the main breaker.

Box with a flywheel that spins up to very high RPM using a motor/generator, then change it from motor to generator using a higher number of windings and then dumping all the energy accumulated in a couple of minutes back into the local grid in a few milliseconds. Probably better to use 2 flywheels so the forces cancel out otherwise the whole thing might come apart.

You could connect this to any wall socket in the company and it wouldn't be much bigger than a suitcase or even fit in one.

If the pulse is short enough it will probably even be re-usable, unlike the power supplies in everything connected to that particular bit of the supply rail. The question is how long you can sustain the pulse, longer = more damage but also more chance of damaging the device itself.