Mods: yes, I know there's a computery subsection, but this is waaay more electronics than modern PC-ness usually goes into. I'd rather not argue (that usually doesn't go so well) so please read this post in full (skimming doesn't count, I hope you understand why...) before you move it. This is a "help me help you" kind of thing

I'm trying here, really!
This is, at 33, making me feel like an angry old guy villain on Scooby Doo. "You meddlin' kids, with yer dang USB-C cables an' your special power distribution 'n' chargin' modes an' yer smartphones and Androids an' Firefox extensions an' [incomprehensible muttering] -- get off my friggin' lawn and DON'T COME BACK!!"
My idea of a good time spent livening up a boring afternoon is often to take an eBay-issue stick computer (HK/CN "Intel Compute Stick" clone, at least by way of form factor) or "Mini PC" (basically the same stuff but in a Roku-style form factor instead) and throw a power supply, keyboard, and display at it from the Junk Pile of Ultimate Randomness that is my closet space (LOL). This usually ends in a combination of two ways: one, I spend money on eBay on little bits of flotsam that I didn't expect to need but wind up needing anyways; and two, I do in fact eventually manage to club the sorry kludge-bag of parts into actually working

Most of the time, power for these things is 5vDC throughout. Nice to have only one power rail!
However, this time I'm staring down a wee techno-beastie of a slightly different sort. I recently bought an HK/CN-origin "no-name" USB-C multi-converter type gadget for my phone. Phone, FWIW, is a Samsung Galaxy S9. The gadget is sort of like those USB-C "universal laptop dock" type things, but for the phone. A male USB-C port witha deplorably short cable goes to a housing with two USB 3.0 type "A" ports, a full-size SD card slot, a "TF" (MicroSD) card slot, and an HDMI port. I've pried it open and looked at the guts... it's structurally a USB 3.0/3.1 hub chip (Genesys Logic GL3224) with a USB 3.0 SD card reader chip (VIA Labs Inc VL813-Q7) and USB-Type-C Alt Mode DisplayPort bridge[?] chip (VIA Labs Inc VL100-Q3) hanging off two of the four ports of the central hub chip. There's also a DP-to-HDMI bridge chip (Parade Tech PS176HDM) in between the DP chip and the HDMI port, because otherwise Bad Things Would Happen.
Ultimately what I'm looking here is a way to power my phone and the USB phone-dock-thing (I *swear* that's a technical term!) at the same time, from a 5vDC source. I have a 5v 6a power brick in mind

"Normally" (i.e. in Yonder Good Olde Days of USB2.0 and earlier) I could just splice together a simple wiring harness. 5vDC in via barrel jack to a MicroUSB port for the screen, and wires spliced into the cable (or, more likely, wires bodged onto the dock-side PCB connection for the USB port headed towards the phone) for the dock and phone. If I wanted to dangle a second hub off it (extremely likely!), and I also wanted touch input from the LCD (it's a Waveshare-knockoff 7" IPS LCD with capacitive touch, meant for a RasPi... 1024x600, works for me! I like small screens...), I could cut the red wire out of a regular Micro-USB to USB-A cable and hang that off one USB 3.0 dock port, with the hub on the other, its cable cut in similar fashion and wires soldered onto its PCB for extra power delivery.
That said, this is USB-C and that's a whole new ball game indeed

Ultimately what I want to know is -- can I splice in extra power the "old fashioned" way, maybe with a Schottky diode on the phone side so that if it gets the wrong idea nothing goes KABOOM

(FTR, for that I have RK44 diodes and SR260 diodes -- which do I want here?), or do I need some fancy schmancy "active" solution like an extra flipping hub or something?
...oh, a note about screens -- if the one I have doesn't work, I can save up for better. Either way, I'd prefer to find out myself, so let's ignore the tiny resolution/size/etc for now, please!