I guess it depended on what kind of troops we're talking about. The leitourgiai system would surely be an adequate system if a polis wants to equip a fighting force to defend itself. If we're talking about a Diadoch's royal army meant for campaigning and fighting enemy armies in the field, then I guess he would partly equip his forces by himself (especially cheap levy phalangitai like machimoi or pantodapoi, since they were poor and the king needed them in large numbers, and the heavy elite units) and partly have his more professional troops, consisting of wealthier military settlers like the pezhetairoi, equip themselves since they got the funds themselves and probably equipment was handed down from father to son. Maybe the Seleukids would also draw upon the old recruitment system of the Persians having Persian nobles provide and equip fighting forces.
At least that's my guess. No claims on historical accuracy here.