Older motherboards use 20-pin connectors, while newer power supplies use 24-pin connectors. An adapter resolves the compatibility issue cost-effectively. * Why Not A (Adjust the input voltage): Input voltage adjustment is unrelated to connector compatibility. * Why Not B (Install a modular power supply): While modular supplies are versatile, this doesn't address the connector issue directly. * Why Not C (Rebuild the failed power supply): Rebuilding is costly and complex compared to using an adapter. CompTIA A+ Exam Reference: Core 1 (220-1101), Section 3.4, power supply compatibility.