PSU Problems

On Monday mys PSU stopped working. It is a Corsair TX650 v2.  i went through many steps to test it and it would not work.  I waited a day to see if that would help.  It did not.  I went to Corsair Support and got the express replacement.  The new one today and I tested both PSUs and they both work.  I have to send them my old one.  Is there any way I can prove that it did not work and what should I do?

Well, you already have the new one, so just send them the old one, and don't say anything.

Will they actually check it?

Probably not. Even if they did, what are they going to do, ask for their working unit back so they can send you this working unit?

For the express return they make you put in your credit card.