As far as I can tell, standard low-current 5V USB connectors (and cables) could be replaced with normal 3.5mm TRRS or TRRRS audio connectors (and cables).

These should be able to handle about as much wattage as micro USB, but not as much as baseline USB-C, which apparently allows more current in its baseline 5V spec.

But instead of wiring new connectors to USB, it would be better to design a new standard that’s also compatible with TRS connectors and cables, while also safely supporting traditional 3.5mm inputs and outputs (like headphones). Mono TS cables might need to be rejected by devices, due to the risk of shorting a circuit when unplugging from live power.

There would need to be standardized circuitry in supported devices, to detect when they are connected to each other, before allowing power mode to be activated.

“Fast charging” over USB requires special USB-C cables, rated for higher loads than the baseline 5V spec. This heavier-duty spec is called “USB Power Delivery,” which can go beyond 5V. Devices also need to detect which cables are connected, in order to limit power accordingly.

Like USB-PD, 3.5mm Power Delivery would also require specialized, heavy-duty cables for “fast charging.” These could even carry more wattage than USB-C (because 3.5mm connectors have more space for possible electrical contact). USB-PD currently goes up to 240W, so 3.5mm PD could go that high, or higher. Good for stuff like power tools and ebikes.

Maybe 3.5mm PD shouldn’t have such a similar name to USB-PD, because it’s confusing how USB has power connectors that aren’t “PD” - whereas 3.5mm would have “non-PD” audio cables that only handle power in “PD” connectors. Instead, we could call it DCS, for “Data and Charge in Stereo,” or “Direct Current over Stereo.” We can call it “class 1” or “level 1” when we use regular TRS audio cables, with higher classes/levels for heavier-duty DCS power cables.

USB-C offers more individual contact points than a 3.5mm connector, so the highest-class DCS specs might require TRRS/TRRRS configuration (or even more specialized customization) in order to match the heaviest-duty USB-C.

A baseline 3.5mm audio cable (class 1 DCS) would still not be able to carry as much current as a baseline USB-C cable. Giving the user a second DCS connector could let them use a pair of 3.5mm audio cables, to get closer to the power of a single baseline USB-C cable (if they have 2 audio cables and no heavier-duty DCS cables).

It might be safe to use a baseline voltage higher than 5 with regular audio cables, which could bring class 1 DCS more in line with baseline USB-C. However, it might also be a good idea to match USB’s 5V, just in case it ever helps with compatibility.

Incidentally, allowing dual-connector use for heavy-duty cables could potentially allow 2x (or more) the 240W limit of USB-PD, so, 480W (or more).

The spec could limit single-connector use to much lower wattage, with dual connectors needed to unlock the maximum amount. This might help with safety, and also help promote the use of dual connectors by manufacturers.

The best thing about dual connectors is, they let you have a backup when one wears out or breaks.

Of course, it’s nice to have possibilities like plugging in headphones and charging at the same time, or plugging in 2 pairs of headphones at once, without carrying hubs/splitters around.

Separate cables could also be used as an intuitive way to control charging speed. Just plug in one regular audio cable, no second cable or heavy-duty power cable, to get a slow overnight charge, with minimal thermal stress on the battery.

Low-end devices might limit their charging speed to DCS class 1, using a regular audio cable, like how some things still use baseline USB instead of USB-PD.

When a DCS standard is actually created, manufacturers should adhere to a color code or something for the different power level ratings, to make it easier to tell which is which. So far, that’s been a missed opportunity for the old USB-PD standard.

All DCS connectors should be mandated to maximize compatibility across all cables. That’s also been a missed opportunity for USB-PD, with, for example, laptops that cannot charge off regular phone chargers, due to mismatched voltages. Class 1 baseline DCS voltage should be usable in any DCS device where it could be feasibly integrated - e.g. trickle charging, in pretty much any device with a battery.

Multi-core insulation should be discouraged in DCS-compliant multi-line cables. If a connector wears out, why should we waste perfectly good wire by having it bundled around itself in a mess of layers? Keep that copper readily reusable.

Avoiding multi-core insulation might also help sometimes with telling which cables are which, at a quick glance.

Devices with DCS connectors should be considered non-compliant if they lack analog audio/video input/output modes in devices which should be able to handle each.