Years ago I ordered seeds for Kampong Mauve online from some Thai website, I have one tree in a container, on the balcony at work, and that little devil put out all kinds of fruit. I have heard that Sugar apples were shy bearers, or that you needed to mess with pollinating etc. they are not big fruit, biggest one I got was about the size of a Valencia orange. tree has about 2-3 fruit on it now with more flowers. I hardly take care of it, just water, some fertilizer once a year. seems to put out fruit, 3 or more times a year. very productive. I can only imagine what it would do in the ground with better care and more sunlight. only gets about 4 hours direct sunlight in the afternoon.
My biggest problem is catching the fruit before they drop, they go from not ripe, to ripe, in one day, so as soon as they turn purple, I get a plastic bag or net, and tie it to the stem, if I don't it will be splattered on the ground.