A testing method and related system enables a power management device to power-on or power-off a second electrical device via a first transmission interface of a first electrical device. The first electrical device sets power-on and power off times of the power management device. The first electrical device sends a power-on or a power-off control instruction to the power management device via the first transmission interface based on the set power-on and power-off times to power-on or power-off the power management device, and the first electrical device performs a timing process. The second electrical device executes a corresponding power-on or power-off process based on power statuses of the power management device. The first electrical device determines whether the second electrical device returns with a power-on or a power-off testing signal as a testing result within a predetermined time during the process of timing.