The separate power supply (e.g. VDDA=5V, VDDD=3.3V) is acceptable for not only PSoC4100S Plus, but also other PSoC devices.
This is for better analog performance in a mixed-signal circuit design. In this case, we have to make sure that VDDD ≤ VDDA.
Please see the following documentation.
AN88619 PSoC 4 Hardware Design Considerations Section 4.1 Power Pin Connections
AN57821 PSoC 3, PSoC 4, and PSoC 5LP Mixed-Signal Circuit Board Layout Considerations Section 5 Multiple Power Domains