A server with redundant power supplies fails to gracefully shut down during a power outage. Which hardware tool should a technician use to troubleshoot this issue?

Using a load tester is the most appropriate action for troubleshooting a server that fails to gracefully shut down during a power outage, especially in a configuration with redundant power supplies. A load tester allows the technician to simulate the power conditions under which the server operates, ensuring that each power supply is functioning correctly under various loads.

By employing a load tester, the technician can determine if the redundant power supplies are capable of handling the total load of the server when one supply fails or is taken offline. If the server can't maintain power with the remaining supply, this might indicate a failure in one of the power supplies or an inadequate power handling capacity. Additionally, the device helps identify potential voltage irregularities, which may affect the performance and reliability of the components inside the server.

The other tools listed serve different functions. An OTDR (Optical Time-Domain Reflectometer) is used for testing fiber optic cables, which is not relevant in this case. A loopback plug is for testing network interfaces and does not address power-related issues. A crimper is used for networking cables and connections, which is also unrelated to power supply troubleshooting. Thus, the load tester is the dedicated tool suited for confirming the condition of power supplies in a server environment.