Visual Signs of Capacitor Failure - Bulging

So we can have training aids at work, I have some boards that I have fished out of the recycling bin.  The characteristic failure of the output modules is one or two capacitors just like you show.  I replace them and the boards are good enough for training.  Great job taking a picture that shows the bulge.  That's not as easy as it looks. 

Jan Cumps said:

It's definitely bulging: It's the first time that I see one where the symptom is so obvious. I had others that failed or leaked. But never such a visible sign of the internal pressure effects.

Exact opposite here, I've seen far more signs of bulging than leaking.

The top isn't flat anymore....

I always find fun in looking inside electronics.

Yes the bulging top is always a give away.

beacon_dave I agree with the bulging more than leaking, but definitely more "no visible indication" than anything else.

dougw A design feature that actually does what it's supposed to.  Imagine that! 

Does anyone know the range of pressures that would cause bulging versus venting in a typical cap?

today I learned: they’re supposed to bulge on top!

Very common in consumer electronics such as TVs, stereos, etc, because of limited warranty periods & modular design: if the power supply stage has a faulty cap, just replace the power supply PCB only and you're back in business quickly. On the other hand, I've seen bulging caps operate for quite a long time (perhaps they were oversized to begin with?)

I'd appreciate a design review!

Scenario is, I need a PSU (500 mA, about 13.7V output after the regulator). This is a one-off project but I won't have access to it so it needs to be reliable. The ambient temperature may reach 40 deg C. The PSU will be switched on and off maybe a couple of times a day. The load may peak to 400 mA, and on average will be 300 mA.

I'm using a 14V 15VA transformer, operating from 50 Hz mains. (It's a linear PSU, for low noise reasons).

The capacitors are rated at 100 kHz, so some extrapolation is needed.
I believe the three electrolytics are selected to operate comfortably well.

I'm most concerned about whether the 47uF polymer tant is suitable or not. I've never used such a part. The polymer tant is supposed to fail in a benign way compared to normal tantalums, which is good to know, but I still want a reliable design. The TCN.. part is supposedly suitable for 'bulk decoupling of SoC').

Would you/have you used a polymer tant in a PSU? Recommended or not?
I've not constructed this, but the PCB is ordered. If I replace the cap, it will ideally need to be a similar footprint (7.3 x 4.3 mm component size). I suppose I could piggy-back a couple of capacitors as long as it also still looks tidy too (this PCB will be visible through vents).

If it's really not recommended, I could go with this 22 uF ceramic cap, it will fit. Thoughts?