You can't change the laws of physics...
I don't know if it's a law of physics issue but understand there could be engineering challenges. In my mind, there are a few issues:
1. Since power is part of the connection negotiation, each port can provide the required power by itself, and there is more than enough system power in a Studio, could this be a software/firmware issue that could be resolved in a future update (perhaps the firmware is assuming the hardware limits of a MacBook or Mini but actually the Studio hardware can handle more)?
2. If this is a hardware/electrical engineering limitation, what were the design trade-offs that necessitated it? Why is this system outfitted with a 480W power supply if even its max configuration only consumes 270W internally?
3. Why doesn't Apple document this limit publicly? The spec pages for each Mac documents all the permutations of monitor resolutions but says nothing about limits on total Thunderbolt power usage even though I'd say such power limits are less intuitive for most people. How would any typical buyer know if it is 15W or 30W or 60W and/or if the front ports count?
Obviously that isn't reasonable for their to be multiple pairs of 12mm power distribution traces in a logic board the size of the Mac Studio/Mini/MBP, so there are likely to be compromises... 😕
Trust your electrical engineering estimates but still not convinced the issue is physics. We know the system has 480W of continuous power and we know it can provide 15W (5V x 3A) to any of the 4 rear port. Plus it appears that it can provide 2x15W to any two ports (it doesn't appear to matter which two so there doesn't appear to be any pairing/shared constraint like there was on the Intel-based Macs). From that I would conclude the traces/wiring are thick enough to support 3A to each port but they are sharing a 30W power bus (or perhaps 37.5 or 40W bus since 2xTB + 1xUSB also seems to be supported) if this is indeed a hardware/design limitation.
If so, it's unclear to me why they wired it that way rather than giving each port its own 3A power connection. I am sure Apple engineers know what they are doing and all else being equal would have preferred not to have this limitation so guessing there was a trade-off that had to be made within the other engineering constraints (e.g. time-to-delivery, etc).
Also note that there are single PCIe 4.0 cards that can support 4xNVMe drives and most desktop PCs support multiple PCIe cards each drawing 25W (or optionally 75W) not to mention allowing for auxiliary power outside the bus. So I have to believe it's possible to route 4x15W to 4xType-C ports though appreciate perhaps not easy given other system constraints.
Workaround: Only use a couple of ports for 5A bus powered devices, as and when they are needed.
For regular permanently attached storage or outboard signal processing equipment use self-powered enclosures.
Agree that's the workaround for now (and probably foreseeably). It does mean a user has to buy two TB5 hubs ($200-250/each) for an otherwise suboptimal solution -- one that aggravates the octopus problem of lots of external devices now with extra docks and cables each adding another point of failure. Not the worst problem but I'd be disappointed if I spent $10K on a system that couldn't power four external SSD without keeping several hubs strewn about just to power them.
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