Final answer:
To confirm if insufficient power is causing intermittent lockups and system errors in a desktop computer, a technician should use a multimeter to measure the voltage output from the power supply.
Step-by-step explanation:
When a technician suspects that a desktop computer is experiencing intermittent lockups and system errors due to insufficient power to the motherboard, they should use a multimeter to confirm this hypothesis.
A multimeter can be used to measure the voltage output from the power supply and ensure that it is providing the correct amount of power to the motherboard.
By using a multimeter, the technician can determine if insufficient power is the cause of the computer's issues and take appropriate steps to address the problem.