T2 or iodine (some converts to T2) is the only one that provides reliable improvement, one dose every 21 days. Cumin is an effective PEM blocker for me, but I don't know if that qualifies as a supplement. Other supplements, such as l-carnitine, apigenin and thiamine provided some benefits for a limited time, then stopped having a noticeable effect.
Since we all seem to have a wide range of side effects from the core ME/CFS dysfunction, which supplements are effective depends on the individual.