Split input voltage 19.5V to a 5V and b 12V?

I have a little DIY project. I would like to use my old notebook power supply to operate a) my Raspberry / SNES and b) my DIY LCD screen.

So I have 19.5V / 4.7A as INPUT and need two OUTPUTs:

a) OUTPUT 5V / 3A

b) OUTPUT 12V / 4A

How and with which components can I do this?

With a step-down / DC-DC converter with sufficient power

I suppose he even needs 2 of these things.

A DC / DC converter from 19.5 to 5V

and

a DC / DC converter from 19.5 to 12V

Needless to say that these must be adjustable.

A fixed voltage regulator 7805 and 7812, but I'm not sure if the 3a can do it

Thanks first of all. So far I was already. These step-down converters abound. But I don't know if everything always works that way (physics was a long time ago). And then I don't know whether the current is sufficient.

Can I connect two DC / DC converters to one input? Split it, so to speak, and the same thing arrives at both 'branches'?

No with this series 78xx fixed voltage regulators, 1A is over.

The adjustable voltage regulator LM350T can, however, up to 3A (cooled).

and the adjustable LM 1084, which can up to 5A, but really costs coal.