A technician replaced a failed PSU on a high-end workstation PC. Now, the PC fails to POST and does not stay turned on for more than five seconds. Which of the following power connections was most likely forgotten during installation?

The 5V connection is typically used for powering smaller components like USB devices and some peripherals, but it is not essential for the main power needs of the CPU and motherboard during the POST process. Therefore, forgetting the 5V connection would not lead to immediate failure to POST and is unlikely to be the cause of the issue described.

The 120V connection refers to the AC power supply that feeds the power supply unit (PSU) itself. While essential for overall power delivery to the system, the presence of 120V would not directly explain the failure to POST if the PSU is functioning correctly. It is unlikely that this connection would be forgotten if the technician has replaced the PSU.

Like the 120V connection, the 220V AC connection is related to the power supply unit. However, this is dependent on the regional power standards and is not applicable in all locations. The absence of this connection would prevent the PSU from receiving power altogether, but if the PSU is working, then it would not be the cause of a quick shutdown during POST.