How can I test a USB switch and hub for compliance with USB power standards (e.g. no backfeed)?
The test for backfeed is fairly simple. You need to make a dummy USB port with VBUS, D+ and D- loaded with 15 k resistors. When you plug your hub-switch combination into this &quot;fake&quot;/test port, voltages on any of the pins (VBUS, D+, D- ) should not exceed 400 mV.
See the Back Voltage test description here. For schematics of the test fixture, see this answer, USB IF specification for back powering Hubs .
For general scope of USB 2.0 electrical tests for USB-IF compliance, see this document.