Looking at more images of Sedum, I found one called Sedum liebmannianum that is perhaps a better match, but still not quite right.
When I googled Sedum liebmannianum, I found this photo by Stan Shebs, and two other photos that he had taken. The flower stalks on his examples are much thinner than mine, and my yellow blossoms seem to be formed in a rounder version.
I obviously have a lot to learn from the Sedum kingdom.
Does anyone have a clearer idea of what my Sedum could be?