Final answer:
The maximum acceptable variance from specified DC voltage levels when using a voltmeter to diagnose a computer power supply is usually within ±5% of the nominal voltage.
Step-by-step explanation:
When diagnosing potential power supply problems in computers with a voltmeter, the maximum acceptable variance from specified DC voltage levels is generally within ±5% of the nominal voltage. A computer power supply often outputs several different voltages, such as 12V, 5V, and 3.3V DC. For instance, a 12V rail should read between 11.4V and 12.6V. If the DC voltage levels read by the voltmeter are outside of this range, it may indicate a problem with the power supply that warrants further investigation or replacement.