When dealing with dates in SQL Server, the ISO-8601 format is probably the best way to go, since it just works regardless of your language and culture settings.
In order to INSERT data into a SQL Server table, you don’t need any conversion codes or anything at all – just specify your dates as literal strings
INSERT INTO MyTable(DateColumn) VALUES('20090430 12:34:56.790')
and you’re done.
If you need to convert a date column to ISO-8601 format on SELECT, you can use conversion code 126 or 127 (with timezone information) to achieve the ISO format.
SELECT CONVERT(VARCHAR(33), DateColumn, 126) FROM MyTable
should give you:
2009-04-30T12:34:56.790