The information you were given in that other thread is absolutely incorrect. If it were, you'd have to put twice as much power into the input of the supply as you get from the output, which is NOT the case. The supply will NOT be dissipating 250W. The only significant power dissipation in the supply itself will be in the bridge rectifier, which may be dissipating a few watts, and that only when the supply is providing high current to the motors, which it should never be doing for very long. It should be heat-sinked (i.e. - mounted to a metal plate, smeared with silicone grease at the interface).
Those are some gnarly looking capacitors. How old and.or abused are they? Old electrolytic caps do not perform well, and can go "boom". On the blue plastic sleeve you should see a minus sign, or a string of them, running the length of the capacitor, near one of the terminals. That is the minus terminal. Do NOT power it up unless you are certain it's connected correctly, or it WILL go BOOM as soon as you apply power!
Regards,
Ray L.