You are referring to two different products made by two different companies. The reason why Maxspect sells the pump by itself is because their controller allows you to run two pumps at once with one power supply. So when you purchase the single pump, it is with the intent that you already have an pump with the advanced controller so you only need the pump. You don't need the power supply nor the controller.
The IceCap interface is a 3rd party controller created by a 3rd party company. They are only providing you with the interface module. It is up to you to purchase the parts you need. If you already have a first generation gyre, then all you need is the interface module as you already have the power supply. If you purchased the second generation gyre with the controller but decided that you rather connect it to the APEX, then you only need the module as you already have a power supply. But if you purchase the second generation pump only (the one that the manufacturer intended to be used as a second pump on an existing controller and pump) then you will need to purchase additional parts to make it work. In this case, you will need to purchase the power supply.
We are sorry for the long response but we feel the responsibility to clarify the issue and why the products are sold the way they are. They are made by two different companies and each company sells the product according to what works for them. Maxspect will sell the products based on what other maxspect products do and IceCap will sell the module. It is up to the consumer to know what you need or ask if there are additional parts needed.
You can purchase the additional power supply by using the following link:
http://www.coralvue.com/maxspect-gyre-power-supply