This is a photo of the two units. For clarity:
STEEL P+ STEEL P+
When I tested the new power supply with the LM350K at the left, I quickly noticed something: Maximum output current was just under 2 amps. Of course I checked all parts, and of course the heat sink, but I found nothing: It was the regulator itself who was limiting the maximum output current just under two amps. Why?
Once of the features announced in every LM350 datasheet is:
Guaranteed 3A output current
The same datasheet explained how the maximum output current is available only with a limited range of input/output voltages:
All conditions were meet, but output current never went over 1.9 amps, so I decided to test the second unit, the one at the right of the above photo. The second unit worked just as expected: Maximum output current is 3.6 amps, more than the guaranteed value (3 amps) but somehow under the graph values (4-5 amps). Because 3.6 amps is above the guaranteed value, I declared finished the power supply rebuilding.
Why the first LM350 did not reached the "guaranteed" output current? I don't know. Maybe is a defective part, or maybe is a counterfeit. With a limit current of 1.9 amps it resembles to me more like a LM317 than a LM350.
Finally, some advice: LM317, LM350, LM338 and similar adjustable 3 terminal voltage regulators are prone to self-oscillations when bypassed with ceramic capacitors. Use always electrolytic capacitors with these regulators.