Custom DC-DC converter help needed: Turning it on with +3.3v

I'm working on a case mod for an original Xbox, and need to replace the original PSU with something significantly smaller.

The PSU needs 4 outputs:
+5v, 13.6A Always on
+5v, 3.6A
+12V, 0.8A
+3.3V PSOK
The last three signals should be controlled by a +3.3V signal received from the xbox when the power button is pressed.

As far as obtaining the voltages, my plan is to run a 5v line to the xbox.
Inside the case will be a TI ptn04050c to get the 12v line, and a (likely overkill) TI pth08080w to get the 3.3v PSOK signal.

My problem comes when I try to make the xbox behave like normal. I've been researching different transistors, and trying to figure out what I need to be able to get from them, but the more I read, the more I confuse myself.

What I need to know is:

What is a size efficient way to switch power on in three lines, with the load between the switching device and ground, using a 3.3v signal?
More specifically, Since I imagine I would need to use transistors for this, what type would best suit this project, and what should I look for in specs on digikey or mouser?
I thought I had things figured out, but then when I went to look for parts, all the terminology confused the bejebus out of me.


More Info

Dedicated project thread:
https://forums.modretro.com/viewtopic.php?f=64&t=9731

TI Regulators mentioned:
https://www.ti.com/product/ptn04050c
https://www.ti.com/product/pth08080w

One idea for the power control circuit:

Awesome! Now on to the second bit of my problem:

ttsgeb said:

More specifically, Since I imagine I would need to use transistors for this, what type would best suit this project, and what should I look for in specs on digikey or mouser?
I thought I had things figured out, but then when I went to look for parts, all the terminology confused the bejebus out of me.

Click to expand...

So I understand that the MOSFETs in the diagram need to have a max S-D current of

>0.8A @12V
>3.8A @ 5V

and I think need to have a saturation voltage of -5V
How do I put this in terms that I can use to find the parts from a distributor like Mouser or Digikey?

I'm kinda new to the whole circuit building thing, in case you can't tell.

On second thought, see the new circuit, now we need only one P-Channel MOSFET. Can you solder tiny SMD circuits? E.g. for the P-channel MOSFET: IRF7424PBF, SI4401BDY-E3, SI4463BDY
(PTH08080W and PTN04050C included)
https://www.ti.com/lit/ds/symlink/ptn04050c.pdf
**broken link removed**

- - - Updated - - -

In practice aiming low power dissipation for the MOSFET transistor we may use two transistors in parallel.