Hans writes -

I posted a quick How-To for the PowerSwitchTail. Thanks for including the extra components, they worked like a charm with a low-current digital output pin. Adapter Circuit – The PowerSwitchTail requires 40ma to control the internal relay. The IO-204 supplies 20ma on each of its 4 I/O channels. In order for the IO-204 to trigger the internal relay of the PowerSwitchTail, you need to connect a simple current adapter circuit. If you buy the PowerSwitchTail from Adafruit, you will recieve the necessary parts to build the adapter circuit.