Why the obsession with output ripple voltage of SMPS?

[cupoftea]

Hi,
Why is it that most Engineering companies who are looking to get a Switch Mode Power Supply designed for them
are only interested in the voltage ripple on the output volts?
They fear that an SMPS will destroy the operation of their system due to the SMPS noise.
As long as an SMPS has enough capacitance so that the output caps are not over-ripple currented, then the ripple that you get will generally be
fine and not too noisy in 98+% of cases.

Even 3v3 microcontroller or FPGA rails don't need to have ripple less than 200mvpkpk in general. As long as any analog reference voltage is ripple
free then its fine.

Yes you get some inamps that need super low ripple but they just use a low power rail which can be heavily filtered...so the ripple on the
main incoming power rail is irrelevant.

The actual noise problem of SMPS is the common mode noise that they give off...and this cant be measured on the scope.

So why is the world so obsessed with SMPS output ripple voltage specs?

 

[andre_luis]

In addition to the SMPS intrinsic output swing, there will be many other devices on the board adding their our contribution to degrade the power bus; since these artifacts are assynced each other the interference could either cancel or add, so why not concern on that?

 

[dick_freebird]

Because every damn thing has a radio on it now?

Because they don't know what aspect of delivered noise matters, so they fixate on the one that's published?