I guarantee you that Twinkie is not a USB power source. From the USB charger and device's point of view, it s a pure pass through. It was designed by hardware engineers and electrical engineers on the Pixel team whom I trust completely.

It is meant to be a diagnostic tool, so the USB Micro-B cable that comes out of the side is purely for allowing communication to the STM32 microcontroller that does the actual sniffing.

See this block diagram : https://a77db9aa-a-7b23c8ea-s-sites.googlegroups.com/a/chromium.org/dev/chromium-os/twinkie/Twinkie-diagram.png

You can examine the actual schematics and layout in close detail on the twinkie page if you want too.

If you don't trust my tool, then fine. I've got this on order today that is much cheaper and you can buy yourself : http://www.amazon.com/gp/product/B00ICR1UB6

I'll rerun my test on this.

The Dell adapter is this : http://accessories.us.dell.com/sna/productdetail.aspx?sku=492-BBIB&ref=meekosystems

It's a 10W adapter (2A x 5V), and using a compliant cable, Bullhead pulls just below 2A.