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IIRC USB Power Delivery requires to provide 5V and 12V if you want to provide 20V. According to their FAQ question about compatibility with Microsoft Surface an
by anonymfus 13y ago
IIRC USB Power Delivery requires to provide 5V and 12V if you want to provide 20V. According to their FAQ question about compatibility with Microsoft Surface and Chromebook Pixel (https://www.kickstarter.com/projects/215201435/dart-the-worlds-smallest-laptop-adapter#project_faq_87083 https://www.kickstarter.com/projects/215201435/dart-the-worl... ) they don't have 12V support. Probably they are not ready for USB 3.1.
- userbinator 13y agoI'd guess 12V is for lower-power devices, where (slightly) cheaper 16V-rated (the next step below 25V) capacitors can be used. The other parts (switcher ICs and MOSFETs) are usually rated for much higher, and the system would be fine with a 20V input if it weren't for the 16V caps. E.g. the EEE 1000HE uses a 12V adapter, and it has 16V caps in its power circuit. Probably the same for the Surface/Pixel.