I often wonder to what extent it will be fair towards your former employer when you add its company name to the list of your previous jobs. I think in that case a new employer could implicitly acquire some advantages from the previous one.

The point is, when you state in your CV that you are familiar with PostgreSQL and have some experience with it, it will hardly trigger any questions that fall outside the scope of Database domain. Indeed, it might be a pretty different situation when your new employer knew that you worked for its competitor in some ways. In that situation, it would be much more likely that you were questioned not only for the respective domain but also for an exact internal structure of ways of dealing with tasks similar to those of the new employer.

Moreover, openness and eagerness of an applicant in that regard might be the most determinant factor in offering a job. Thus, I think this issue would become more obvious and objective so that it would influence the way we are making the list of our previous jobs.