That is what I was trying to point out: Not oscillating does not mean more stable, it can be the opposite.
Even assuming perfect (no error) multimeter, it still needs to round or truncate the value to the available decimal places.
So again the same examples I gave:
1. PSU 1 real analog value oscillates between 15.134 and 15.136 (a 0.02 delta). The minimum will round to 15.13 and the maximum will round to 15.14, so your multimeter will oscillate between those two values.
2. PSU 2 real analog value oscillates between 15.196 and 15.204 (a 0.08 delta). Both the minimum and maximum will round to 15.20, so the multimeter will display a steady 15.20 value.
So you see how PSU 2 that oscillates 4x more, show a steady digital value,
while PSU1 which oscillates 4 times less does display oscillating digital value.