The Power XR products use a GM amplifier, and the analog products, like the Power blocks, and the SP6133 family all use a true amplifier. There are some benefits to one versus the other. In an analog system with a fixed reference, the GM based trans conducted amplifier will change its gain based upon the feedback resisters. If the output voltage is getting changed there will be a change in gain, and that might be an issue, particularly in a system where changing the output voltage dynamically like in the Power XR product. With the true amplifier the designer can set the external compensation, the impedance is Z1 and Z2, those would be fixed and then the single resister R2 could be changed, and have the exact same control loop as the output voltage is being changed, and this is the type of system that would be found in almost every power supply for say an Intel processor. The GM amplifier implementation in the Power XR product, instead of changing feedback resisters, the engineer actually changes the DAC reference voltage to change the output voltage. In this way the gain term of the GM amplifier, V ref over V out, is now a constant because the engineer is changing both at exactly the same time. As a result the gain is fixed and there is no worries about the compensation or the control loop of the system in the Power XR products.