Hello,

Here I have made some PDF's of the webpages of Tony van Roon about a benchtop powersupply.
It give a good explanation on all parts.

Bertus

 

What should be the standard amount of current for 12 volt output source?

A lab power supply for a beginner, I would recommend starting with 1 amp.
My variable power supplies are 1 amp. The times I've needed more have been rare.

 

The 1Amp supply is a very good start. If you are worried about using your higher current supply, you could get a range of ployswitches (resettable fuses) and use them to limit the current. Have a search on EBay for them. Many are available in various current ratings. You could even have a selector switch wired in to chose the one you want to use.
The RXEF050 will carry up to 500mA and trip at 1Amp.
Of course you could make an electronic current limiter but these are easy for protection.

https://www.ebay.com.au/sch/i.html?....H0.Xpolyswitch.TRS0&_nkw=polyswitch&_sacat=0

 

Of course you could make an electronic current limiter ...

That's one of the endearing properties of the LM317, that without a lot of attention to heat removal, the LM317 will put itself into thermal shutdown before it destroys itself. It's not something I'd want to base a critical design on, but this feature has saved the butts of countless DIYers. I'm one of them.

 

What should be the standard amount of current for 12 volt output source?

There is no standard amount of current either into or out of a 12 volt source.

Consider:
The output of a 50% efficient, unity power factor, 12VDC constant voltage source is connected across a one ohm resistor, while the input to the supply is connected to 240 volt RMS mains.

From Ohm's law, the current into the resistor must be:

\( I = \frac{E}{R} = \frac {12V}{1\Omega} = 12\text{ amperes,}\)

and the power dissipated by the resistor must be:

\( P = IE = 12A \times 12V = 144 \text { watts.} \)

Then, since the supply has an efficiency of 50% and it's pushing 144 watts into the resistor, it must be pulling

\( Pin = \frac {Pout}{\eta} = \frac {144W}{0.5} = 288 \text { watts} \)

from the mains.

Since the mains is sitting at 240 volts, RMS, and the power supply and its load are dissipating 288 watts, the supply will be drawing:

\( I = \frac{P}{E} = \frac {288W}{240V} = 1.2 \text { amperes} \)

from the mains.

Now work out the numbers for the same supply connected to, say, a 2 ohm load, and you'll see that there is no "standard current" into or out of the supply since those currents vary as the demand of the load changes.