@crochat the USB Power Delivery spec that allows up to 100W is only available for USB-C connectors, not USB-A connectors as are used on the D3100. USB-C didn't exist when the D3100 was being designed, which was a while ago since the D3100 is quite old by now. However, note that its replacement model the D6000 has already implemented that solution. The D6000 supports being connected via USB-C or USB-A, and when you connect it via USB-C to a system that supports being charged over USB-C (not all systems with USB-C connectors do, the D6000 will supply up to 60W to the attached system. That limitation is likely based on the power supply the D6000 has and the fact that going over 60W requires higher grade cabling rated for up to 100W, and it's worth noting that the vast majority of USB-C power sources and docks on the market cannot supply the full 100W that the spec allows, nor would most devices use that much power even if it was available. And Dell's other docking stations that connect over USB-C -- such as the WD15, WD19, WD19TB, WD19DC, TB16, and TB18DC -- all supply 60-130W over USB-C depending on the dock model, power supply wattage, and system being used. Dell did something proprietary to stretch the USB PD spec out to 130W to support systems like the XPS 15 models. Speaking of systems, most if not all of Dell's Latitude, XPS, and Precision systems made over the last few years have USB-C ports and support being charged that way, and that capability is also increasingly being implemented on Inspiron and Vostro systems.
As for why a power connector wasn't bundled with the D3100, I suspect that's because the D3100 is explicitly billed as a universal dock, which would include non-Dell systems, and adding a proprietary Dell power connector would make that less universal. Even Dell itself currently has two different barrel-style power connectors implemented on their system, one that's 7.4 mm and another that's 4.5 mm. But I've seen installations where people simply use a zip tie or Velcro strap to keep the D3100's USB cable and a Dell AC adapter cable together on desks.
jphughan
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December 10th, 2019 06:00
@crochat the USB Power Delivery spec that allows up to 100W is only available for USB-C connectors, not USB-A connectors as are used on the D3100. USB-C didn't exist when the D3100 was being designed, which was a while ago since the D3100 is quite old by now. However, note that its replacement model the D6000 has already implemented that solution. The D6000 supports being connected via USB-C or USB-A, and when you connect it via USB-C to a system that supports being charged over USB-C (not all systems with USB-C connectors do, the D6000 will supply up to 60W to the attached system. That limitation is likely based on the power supply the D6000 has and the fact that going over 60W requires higher grade cabling rated for up to 100W, and it's worth noting that the vast majority of USB-C power sources and docks on the market cannot supply the full 100W that the spec allows, nor would most devices use that much power even if it was available. And Dell's other docking stations that connect over USB-C -- such as the WD15, WD19, WD19TB, WD19DC, TB16, and TB18DC -- all supply 60-130W over USB-C depending on the dock model, power supply wattage, and system being used. Dell did something proprietary to stretch the USB PD spec out to 130W to support systems like the XPS 15 models. Speaking of systems, most if not all of Dell's Latitude, XPS, and Precision systems made over the last few years have USB-C ports and support being charged that way, and that capability is also increasingly being implemented on Inspiron and Vostro systems.
As for why a power connector wasn't bundled with the D3100, I suspect that's because the D3100 is explicitly billed as a universal dock, which would include non-Dell systems, and adding a proprietary Dell power connector would make that less universal. Even Dell itself currently has two different barrel-style power connectors implemented on their system, one that's 7.4 mm and another that's 4.5 mm. But I've seen installations where people simply use a zip tie or Velcro strap to keep the D3100's USB cable and a Dell AC adapter cable together on desks.