Google Transliterate (http://www.google.com/transliterate/) now supports Sinhala Language.
I tried entering "subha aluth awuruddak wewa" and below is the output.
By checking this service I found out that it does more work than Traditional Phonetic Transliteration.
It has some prediction (AI) capabilities so that in most times it will show the intended word we needed.
I tried the same input with some other similar services and the output was not accurate like in Google Transliterate.