Explanation: Switching power supplies are known for generating Radio Frequency Interference (RFI). Their operation involves rapidly switching current on and off at high frequencies. These sharp electrical transitions produce broadband noise and harmonics that can radiate and interfere with sensitive radio receivers, especially on HF bands. Therefore, the claim of "no RFI problems" is incorrect; RFI is a primary concern and disadvantage with these devices. Conversely, options A, B, and D describe genuine advantages. Switching power supplies are highly efficient, allowing them to accept a wide range of AC input voltages (A) and readily adapt to DC inputs (B). Their higher efficiency and the use of smaller, high-frequency transformers also make them significantly lighter than linear power supplies (D).