Singapore airlines does provide STPC's provided out of certain markets (I have got them for Sri Lanka and India issue tickets) - provided that the 23 hour layover isn't by your choosing and there are not alternative flights with better connections (for example LAX-MAA). They do restrict this on certain lower fare types in economy. If schedule has another option, but that flight is full or more expensive, you will not be given an STPC - only due to suitable connection not existing. This is handled by the SQ office in the country of issue of your ticket and must be prebooked.