The remark about unity gain is not about stability of the amp itself, but about its place in the loop. Namely, even if the amp is severely overcompensated (say by putting 1000uF from out to -in), it still has gain of 1 from +in to out, which means the loop gain has not dropped to an ideal dominant pole as you might've been expecting with such a large cap.
The solution is to apply filtering to +in so it drops at the same rate.
Compare this, which has G = 1 at high frequency,
![](https://www.eevblog.com/forum/projects/is-550uf-too-big-for-a-power-supply-that-has-cc-limit/?action=dlattach;attach=637588;image)
with this, which has G --> 0 at HF.
![](https://www.eevblog.com/forum/projects/is-550uf-too-big-for-a-power-supply-that-has-cc-limit/?action=dlattach;attach=637582;image)
For an error amp, R2 and R4 --> infty, so that DC error is as nearly zero as possible.
For a pole-zero compensation of course, a resistor is placed in series with C2 and C4.
The zero itself means HF gain levels off; the point of doing this, versus leaving it alone, is you have control of the gain and frequency where this happens, rather than being stuck with wherever G=1 rolls it off at.
Tim