best USB C voltage for triple rails

[buildingBlock5]

I'm designing a cheap power supply for a beginner DIY synth workshop. I want to turn a single USB-C PD source into +12V, -12V, and +5V rails
I’m currently using an XL5430 board for the +/-12V and an MP1584EN buck converter for the 5V.

to keep things stable and easy for beginners, should I set my USB-C trigger to 20V or 28V?
the XL5430 is rated up to 28V, but I’m worried about heat and ripple. also, is it better to tap the 5V converter directly from the USB source or daisy chain it off the +12V rail to keep the signal clean?
I want this to be reliable on a standard 45W or 60W charger. If you've built something similar, what's the "sweet spot" for input voltage to keep these chips from screaming?

 

[ohmsweetohm761]

I tinkered with a similar setup last year for a little modular rig. I powered my XL5430 at 24V using a USB-C PD brick, which kept the heat in check and the ripple low. I’d grab the 5V directly from the USB less hassle and it means beginners won’t have to deal with extra noise following them around

 

[theOhmcoder]

Once experimented with daisy-chaining a 5V from a +12V rail in a small synth project and it resulted in a hot whiny MP1584.
Keeping the USB trigger around 24V allowed me to get smooth +/-12V rails without burning out the chips.
It meant less heat, less ripple, and everyone’s synth was still happy with a standard 45W charger.

 

[Arbie_]

I'd stick with 20V for the USB trigger. 28V (USB-C PD 3.1) is cool, but 20V is standard for almost every 45W/60W brick
t gives the XL5430 plenty of headroom'to create +/-12V without pushing the silicon to its thermal limit.
also, tap the 5V buck directly from the USB source. if you daisy chain it off the +12V, you’re just adding more load and heat to your primary converter for no real gain