If battery-powered, the concern raised by bernard obviously wouldn't exist. He was concerned about a cheap SELV losing it's 'S' and so proposed converting it to PELV, with an RCD protecting it, so any leakage of 230V onto the output of the SELV transformer/PSU would hopefully cause the RCD to operate.That would depend on the potential of the -12V with respect to earth. If battery powered, not likely to be a problem.
Kind Regards, John