using more volts than the electric chair
Well...voltage isn't really the whole story. You really need the voltage and current to multiply to a power, then apply that power for enough time for it to be dangerous. For example, typical static shocks are between 4000-35000V, but they only transmit a few millijoules of energy. By way of comparison, these are similarly sized voltages to those used in primary distribution (i.e., not the lines passing by your house, but the ones feeding those lines), and those can kill you instantly because they carry a shitload of energy.
And in a roundabout way, that's how the electric chair actually works in the real world: it basically pumps energy into your body until you cook from the inside. There are definitely some deaths due to disruption of the heart. The aim of the machine was to demonstrate that AC is dangerous, and the main danger over DC is that AC causes muscle spasms, particularly your heart if electricity flows through it. However, most victims of them are basically cooked to death. The electric chair as it is currently implemented is not a fast or humane way to die. If you wanted to make it faster, you would need a much higher voltage and current pair, which would make the method (more) infeasible from a financial standpoint. (Obligatory: we should not be executing people at all.)
Which is why fractal wood burning IS super dangerous! It requires you to work close to a live microwave (oven) transformer (or one of similar size) and the circuit it is connected to, which could very quickly pump enough energy into your body to disrupt it and kill you almost instantly.