Step 1: Power Supply Operation Sequence.
1. Transformer (C): Initially converts AC voltage, either increasing or decreasing it.
2. Rectifier (B): Transforms AC to DC using diodes for signal rectification.
3. Filter (D): Reduces DC voltage variations for a smoother output.
4. Voltage regulator (A): Stabilizes DC voltage, compensating for input fluctuations.
Step 2: Summary.
The operational sequence is: \[\text{Transformer} \rightarrow \text{Rectifier} \rightarrow \text{Filter} \rightarrow \text{Voltage Regulator}\]
Final Answer: \[ \boxed{\text{(C), (B), (D), (A)}} \]