For testing DC PSUs I just run a passive dummy load, it's basically a heap of transistors, driven by 2 darlington stages and a pot.
Because there are no active components (no opamps) it does not need a battery or PSU to power it, and that also makes it pretty bulletproof;
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It will drift a few percent in current as it gets hot, but that is not usually a problem as in normal use I adjust it to different test currents anyway, or if testing one fixed current it might need a "tweak" of the knob once it is hot.