In below schematic circled point tied to ground too, so the voltage on that point will be 0V or -1.2V?
The schematic is from LM338 datasheet. as a beginner things like this really confuses me, sorry if it's too basic.
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The circled point is not tied to ground, the two wires are just crossing. Wires that join are depicted with a dot on the junction as can be seen in several places in the diagram. If you think about it, there would be no point in joining the wires inside the red circle as it would short out the 1.2V LM113.
What may be confusing you is that there is no need to draw the horizontal wire from the top of the LM113 to the right, it does nothing.
The problem is if you want to drive the regulator to low voltages, it won't be able to get below the reference voltage of the adjust pin (1.24V lower than Vout) without a lower voltage sinking current and allowing the adjust pin to go negative relative to ground.
Using the LM338 in this way is good for a cheap easy supply, but an easy way to heat up the LM338. You'd need to restrict the current on it 100mA would dump 2.5 Watts and heat the part up.