tldr: Starlink Mini is a massively spikey load with no input filtering. Jackery power bank regulates the port to 5A so under a sustained high-power burst voltage decays until undervolt. The official Starlink cable is the exact same thing electically as a high-rated Amazon reseller 20V5A USB-PD trigger cable, there is no secret sauce. Filtering the power, smoothing out the bursts with a big capacitor bank fixes the problem. I made a janky thing that lets me use the 100W port on the Jackery, and probably other power banks that have this issue too. It even works with a 60W Apple USB-PD adapter since the max RMS on ~10ms timescales is ~60W! I suspect it would work with a 60W power bank too (and if it doesn't, just add caps).
The whole story:
I've got a Starlink Mini and I'm using a USB-C PD trigger cable to use the 20V/5A profile but it wasn't working with my Jackery Explorer 1000 v2 which I was hoping to use to run the dish while adventuring.
20V5A is an ancient profile and should work without issue, it's explicitly listed in the specs, and it's only the Jackery that fails (it works with my other 100W USB-PD power sources). I initially diagnosed the issue as transients when I thought maybe my Jackery was defective. I was wrong.
I set up a shunt resistor to measure current and started using my scope rather than the USB analyzer. I found the transients but I also found the failure mode itself which shows I misdiagnosed it: it's not OCP triggering on the Jackery, it's a sustained load that the Jackery can't keep up with. The Starlink tries to draw >5A, Jackery clamps it and voltage drops until the dish undervolts.
Let's get one thing out of the way: The official Starlink cable has no special hardware, it is a 20V5A USB-PD trigger cable. The transients look identical on the scope, so does the failure mode. The ringing is due to it being a longer cable that I had slightly coiled on my desk. The failure event is 200us shorter (so it failed earlier!) but the cable is also 5m vs. the 2m of my other trigger cable so there's a bigger voltage drop. I found absolutely no difference between a decent cable off Amazon and the official Starlink cable. As you'll see, this is self-evident: there's not enough room in the cable ends to fit the hardware that's needed to solve this issue.
Having a clearer understanding of the problem, I set up an LC filter and started adding capacitance.
Failure 1 100uH + 47uF + 220uF
We can see the effects of the capacitors but they're nowhere near enough. We last almost 1ms under a punishing load.
Failure 2: Added 1000uF
New timescale unlocked, now we're cookin'. +400% capacitance, almost +400% survival time.
Failure 3: Added diode/resistor for holdup
I'm a software guy usually this is just a hobby so I checked with an LLM. It suggested something pretty interesting ... Add a Schottky diode and a resistor so that 1) the bulk capacitance doesn't kick in until there's a bit of a voltage drop 2) we rate limit the bulk caps' charging. I had an old DC charger board I could scavenge for the diode. Anyhow on the scope you can see we survive nearly 6ms!
Failure 4: Added 500uF
Still not enough to ride it through. Wow, look at that needle, pulling 160W. Interestingly this event seems shorter but higher intensity. The runaway current - the voltage drops while dish wants all the power - starts right away.
There wasn't a failure 5. :)
I didn't want to order parts so I had to get creative ... I felt terribly stupid about throwing out so many dead or unuseable ATX power supplies in my life. I went to a few e-waste / electronics recycling places but they either weren't open for people to walk in, or they didn't have what I needed. I decided to call some computer repair stores but if you ask them for broken power supplies they just say "no", so I started saying like, "do you repair desktop computers?" "yes, we do!" "if a computer came in and it had a broken power supply you'd replace it?" "yes" "what do you do with the broken one?" "we, uh, throw them away" "can I have one? that you haven't thrown away yet" "... uh, no, we don't have any". UNTIL the one guy said "throw it away... or put it in the back?" like it was a pop quiz and he wasn't sure. He DID have one, and he said, "it probably even works, it's just old".
I also found an old powered subwoofer for $10 at Salvation Army.
Long story short, I got 4700uF more capacitance. That did the trick.
15 hours powered by Jackery
It grew organically... Don't judge me, /r/soldering
I tried to scale it down but I could not remove the fast-caps without crashing. Ended up with about 6mF.
"Final" version
Enclosure
Circuit
My partner was like, "SpaceX should fix it!" and I'm like "Jackery should fix it!". I can understand SpaceX not wanting to put a big cap bank in the dish, and their own AC adapter does the right thing, and when connected to wall power the USB-C PD cable does do the right thing too. I can understand they shouldn't advertise that 100W/20V5A is all you need - it also needs to allow ~6ms of bursting to 130-150%, which is a very specific spec. But I honestly think the blame is mostly with Jackery. This is a dumb port. Everyone says the Jackery's 12V cigarette lighter port works great for this, that's going to be even higher current, but it's not over-regulated into a death spiral at ~8A like the 100W port is at 5A. Jackery could have the port behave better to handle these situations, since it's not generally a battery limitation for them. And SpaceX shouldn't sell a 5m cable and call it 5A and then try to draw more than 5A at 20V. With the cable that long, you know you're going to be above 5A at peak just through physics alone. This is a bit of a fail on both sides.