If our pedals detect a problem with the power supply, the bypass LED with change to magenta (or pink), the pedal will switch to bypass and enter a low power mode.  After a few seconds, the pedal will restart.

The most common reason is that the power supply is not providing enough current.  Our pedals with USB require 250 mA of current and we recommend an isolated power supply.  Note that some multi-pedal supplies are rated at 100 mA except for a couple of high-current outputs.  For example, on the Voodoo Labs Pedal Power 2+ you need to use the L5 outputs (5 & 6) with the DIP switch set to NORMAL.

Many multi-pedal power supplies share current across multiple outputs.  Examples are the T-Rex Fuel Tank, Truetone 1 SPOT Pro, and the MXR DC Brick.  You need to make sure the total current required for all connected pedals is within the power supply's limits.  While troubleshooting, you can disconnect one or more pedals to see if the problem goes away.  For complex setups, the Truetone 1 SPOT mA Meter is helpful to see how exactly how much current each pedal is drawing.

See this article for information about specific power supplies.