What device could Tiffany use to check the voltages of both in the situation that her computer powers off suddenly when she is enjoying some downtime on her new desktop computer, she checks to see if the power cords are still in order? If they are, she feels she can search the power supply in her computer, but her parents inform her that the power outlet she's used has already created problems.
A multimeter can measure voltage from both the power outlet and the power source. This would aid in narrowing down the cause of any power problems. The sole purpose of a power supply tester is to measure the power supply device.