Explanation
According to the CompTIA troubleshooting methodology, the next step after establishing a theory of probable cause is to test the theory to determine the cause. However, before testing the theory, the technician may need to conduct some research based on the symptoms and the possible cause. This may involve consulting online resources, manuals, documentation, or colleagues to find out more information about the power supply and how to test it. Research can help the technician confirm or eliminate the theory and avoid unnecessary actions or damage.
Answer A is incorrect because inquiring about environmental or infrastructure changes is part of identifying the problem, which is the first step of the troubleshooting methodology. The technician should have already done this before establishing a theory of probable cause.
Answer C is incorrect because establishing a plan of action to resolve the problem and implement the solution is the fourth step of the troubleshooting methodology. The technician should not jump to this step without testing the theory and verifying the cause.
Answer D is incorrect because documenting the findings, actions, and outcomes is the last step of the troubleshooting methodology. The technician should not do this until the problem is resolved and verified.
Reference: Troubleshooting Methodology | IT Support and Help Desk | CompTIA