COTS solutions for ±18V DC (or even ±20V) and ±30V PCB-mounted power supplies in the 3-5 Watt range
Assuming you're doing the sort of thing that can live without galvanic isolation, there are plenty of easy solutions. If you don't mind a transformer, here is one of the lowest parts-count (and probably lowest cost) solutions, using the ubiquitous LM2577:



The simpler solutions (as with the cheaper DC-DC converters) tend to have so-so regulation, require a minimum load etc. Be mindful of this if you're up near the absolute maximum voltage input of the load semiconductors- the output voltage could be volts above nominal with a very light load.