It is very important that if a user chooses to use a power supply other than the factory provided one that it can provide the appropriate power.  Even though it make seem to work fine a power supply that can not provide enough current will cause your Relay to act unpredictably and you will likely suffer from drop outs (maybe not may ... but who wants them?)

A third party supply must be able to provide a minimum of 350ma @9vdc exclusively for the Relay.  It will probably turn on with lower but will have problems staying synced.  Higher current is fine (the factory supply provides 500ma @9vdc).

Here's the part that many users miss.  When you plug multiple pedals into a supply you share the total current available (like the DC brick) so there will not be enough current for the Relay.

Isolated output power supplies are prefered because when then are not isolated you are creating a ground loop which will likely add noise/hum/buzz.  That happens whether or not you are using a Relay.