This is just generating the negative voltage for the RS232 transceiver. (Real RS232, not TTL serial.) You don't need very much current, and it doesn't need to be low noise.
The TPS6040x chips (search for TPS60402), or a LM2662, etc will do -- RS232 is one of their design targets. You'll see switching noise at higher loads, so don't plan on using them for anything sensitive e.g. opamps without additional filters.
The old RS232 target was -9V and +9V transceiver outputs from a -12V/+12V supply. Modern stuff usually runs -5V/5V to the transceiver.