I have read that the amperage of the power supply should match the amperage rating of the booster / command station.
Yes, from the standpoint of putting more than 8 Amps of power into an 8 Amp Chief is not going to make a difference since only 8 Amps is going to come out.
Less than 8 amps in is only going to result in that same amount (roughly) out; thus, a 5 Amp power supply will only yield 5 Amps out, even though the system is rated at 8 Amps.
The DCS200 Super Chief is rated at 8 amps.
Which power supplies are recommended for this starter set?
In this case, the only product in the Digitrax line is the 20 Amp PS2012, which means that you're going to have some power left over.
This power can be distributed to other devices, using the YC52 "Y" cable that comes with the PS2012.
It is important that all polarities and "phases" be maintained.
The one major exception to this is the PM42, which subdivides power outputs into smaller subdistricts.
This device must be powered by its own power supply because of the circuit timing issues of the PM42 in relation to other devices on the railroad.