Is it possible to eliminate output ripple of SMPS's by using two parallel SMPS's to produce outphase outputs to each other?
Is it possible to eliminate output ripple of SMPS's by using two parallel SMPS's to produce outphase outputs to each other?

No.

However, some switching power supplies are multi-phase, which means they have multiple power trains in parallel inside.  This is usually done to increase the output current capability, but the phases are also usually run evenly staggered over a cycle to reduce ripple.

Eliminating ripple using two supplies would require each to having exactly the opposite ripple of the other, and then these two exactly averaging.  It should be obvious that's never going to happen.

Other than specifying absolutely 0 ripple, the main fault in your thought process is that the ripple of switching power supplies is unlikely to be something that is symmetric per half waveform.  Your diagram shows sine, for which this would work, but the ripple out of switching power supplies is more spiky than that.  Or, it can be a trapezoid output with fairly sharp rise, then slower decay, or sometimes a slow rise with fast decay.  Changes in the load will also affect the amplitude and shape of the ripple.  These kinds of waveforms 180&deg; out of phase don't average to a flat line.