I have created a tool to geocode large amount Singapore postal codes into X, Y values of SVY21 coordinate system. SVY21 is the Singapore standard coordinate system used by Singapore Land Authority.
You can get the X, Y values of an address by using search function provided in www.onemap.sg. But if you have a few thousands of addresses to geocode, my batch geocoding tool can help you better. You need internet connection to use the tool because the program is the wrapper written in c# to call web service provided by onemap.
Download link: Batch Geocoder Installer
Download the installer and unzip the folder. Run setup to install the tool on your computer. You may need .NET runtime to run the program. After installation run the tool from start menu.
Simply provide an input file containing a column of Singapore postal codes. Give the name and location of the output file where the result (X, Y) values are to be written. Click Run button to start the batch process. It may take a while depending on the number of postal codes you are processing.
Right now, the tool can only accept postal codes as input. In the future, I am planning to extend it to accept whole or partial addresses as input. The source code is hosted on Github https://github.com/zkkmin/BatchGeoCodeOneMap for anyone who is interested to look at it.