Don't get off in the weeds about how an alternator works. You're right about it being 3Φ AC and rectified, but it doesn't matter.
What is important to realize is an alternator is a DC constant current source and time-varying (e.g. with RPM) voltage source.
All that means is when your alternator says it's 100A that means it's typically always 100A but the voltage could be 12.5V or 13.8V or 15V or something else at any given moment. It's not as simple as that because the load current demand is usually a function of voltage, so the current in the circuit may also vary but the alternator itself can be viewed as a 100A storage tank no matter what the voltage is.
The power supply you show is typical of all power supplies. They are constant voltage sources with a maximum current rating.
That just means when you turn it on it will be 12V as long as your load demands 50A or less. If you ask it to supply more than 50A it may react in various ways. Some power supplies will current limit and only ever give 50A at 12V, others might try to give you >50A but the voltage will droop.
How this matter to you is that a DC-DC charger such as the Renogy is at root a power converter. It decouples the input side from the output side so that the voltage and current it puts on the battery it's charging can be completely different than the voltage and current on the input side. All that is true is the power going in is the same as the power going out.
This DCC30S looks to be rated on it's output to do 9V to 16V at a maximum of 30A. That means the most power it does is 16V x 30A = 480 watts.
So it will need to see from the source, whatever that is, is 480 watts plus whatever internal losses it has. They tell you that in the efficiency rating, which is 97% for the DCC30S. So 3% more input is needed to get that output, 480W x 1.03 = 495 watts input.
The DCC30S spec looks to work with alternators from 12V to 16V. So now you have everything you need. The range of inputs will be 495W / 12V = 41.25 amps up to 495W /16V = 31A. That range of inputs will allow it to always produce 30A at whatever voltage it wants to put on the battery. It could be higher or lower voltage than the input voltage.
That power supply you show is 600W and 50A, so that should work fine. You just have to make sure the voltage is high enough and it can source enough current for the demand and it does.
For a point of comparison I use an Iota DLS-45 power supply to run my Victron Orion-Tr Smart. But it's only 18A/220W so my 600W supply is not breaking a sweat and can actually charge the starting battery in parallel.
In the case of what you show the power supply should run the DC-DC directly fine but if you connect it (as I do) as a shore charger for my truck it might not work.
What I'm doing is actually using the DLS-45 with a battery charging controller so it's more like an alternator than a power supply as far as the Victron is concerned. With two charging profiles running (one in the Iota charging my starting, the other in the Victron on the house) weird things can happen if there's insufficient power margins. Voltage on the input may jump up and down as the two controllers butt heads. So if you do something like I'm doing watching it with a volt meter at first might be wise.
As far as alternators, our Toyota alternators (at least on old trucks) usually run pretty low in voltage. So this unit will probably want the high side of current. Mine usually sits in the low 13V region once the starting battery has topped up. Say it settles to 13.2V it'll need to have 495W / 13.2V = 37.5A of available unused current.
A Tundra should have this but I only mention it because an old mini truck or Cruiser with a 60A alternator might not if you have the headlights on and the heater fan and what-not.
