What is the most painless way to get a high current negative voltage power supply from a positive?
The inverting SMPS would seem to be the most appropriate







simulate this circuit &ndash; Schematic created using CircuitLab

When Q1 is on, current into L1 builds, storing energy in it. When Q1 turns off, current continues to flow into L1, and it has to draw this current from D1, pulling charge out of C1, so pulling it to a negative voltage. L1 current falls during this phase, as the voltage across it is negative.

This sort of circuit will happily deliver amps, even 10s of amps. You can use a p-BJT or a p-FET for Q1.

Control consists of detecting the output voltage and changing/stopping the power switch drive.

The usual suspects, Analog Devices, Texas, Linear and Maxim, all have integrated power supply control parts that can be configured to work in this topology, if you don't want to build it from scratch. 

For a particular high load or low ripple application, you can parallel two of these converters driven in antiphase, or even more converters driven in different phases, to get a smoother current delivery waveform into the output filter.