You are just making it worse for yourself with each post.
No, you are wrong.
If you actually hunted down capacitor problems, you'd know the physical venting is the last stage of cheap capacitor failures.
@amirm knows that.
The electrolyte is mostly water and the vents are placed in the "bung" on the base of capacitors. Usually the internal pressure will rupture the bung seal first and a tiny amount of gas (often hydrogen) will escape. This disipates harmlessly. Often the hydrogen can't escape easily as the capacitor is glued to the PCB, so it squeezes up the plastic sheath and the top plastic cap become swollen. People think the can is swollen but it's just the gas under the plastic top cap. The cap may still be fine at this point, although it is a warning for sure.
All the while the capacitor changes its electrical characteristics. An in circuit ESR meter is the best tool to find cap problems long before they physically leak. It's easy and fast (on powered off discharged circuits). Cheap brand caps pretty much always have skyrocketing ESR as they begin to fail. The circuit will still work, but it is degrading fast. The I2R losses (from rising ESR and ripple current) then cause rapid internal heating, loss of more electrolyte and process speeds up to complete failure, often taking out the stamped top vent which is for a catastrophic venting event.
SMPS supplies place a lot of strain on the simple capacitor. High frequency, high ripple current, high temperatures, marginal reserve in design and cheap brands all lead to premature failure.