Transactions

I'm having problems with transactions, lately. I'm checking
power-failure conditions on my psql-based programs, and found that a
simple loop with

BEGIN TRANSACTION
INSERT INTO test VALUES('any #n');
COMMIT TRANSACTION

leaves me with no records inserted at all after an abrupt reset on the
server. The loop is outside the transaction, id est, the BEGIN/COMMIT is
executed every time. Is there any way to assure this, I mean, to
actually write the records and to not rely on the cache to do it?
Because I think it is somewhere floating in the Linux cache and it's
never wrote physically, and when the power is down, everything is lost.
Thank you in advance,

Leandro Fanzone