Low idle power consumption for USB PSU
The efficiency level of AC-DC power adapters is regulated in all developed countries. Here is a good article on the subject from CUI. The adapters are assigned "efficiency level", from "I" to "VI". Products sold in the US should conform to "level VI":



Since 2011 all low-power adapters (&lt;49W) were regulated by IEC AS/NZS 4665 Part 1 and Part 2. They should conform to level "V", with the standby power (aka vampire power, vampire draw, phantom load, ghost load, or leakage) under 300 mW.

With newer "level VI" the DOE requires the low-power adapters (with nameplate power under 49W) to have the standby power under 100 mW.