A server includes a casing, a circuit board component, an assembly component and a power supply. The casing has an assembly channel and a first fastening slot. The circuit board component includes a substrate and a first electrical connector. The first electrical connector is electrically connected to the substrate. The assembly component is located out of the casing and detachably assembled with the casing. The assembly component has a second fastening slot. A distance between the first electrical connector and the second fastening slot is greater than a distance between the first electrical connector and the first fastening slot. The power supply includes a main body and a fastening unit. The main body includes a second electrical connector. The main body is for being movably assembled with the assembly channel, so the fastening unit is selectively assembled with the first fastening slot or the second fastening slot.