If you suspect that the PSU (power supply unit) on your GNSS simulator has failed then it is advisable to contact Spirent Applications Support with a summary of the symptoms you have experienced.
For high-end chassis simulator models, e.g. STR47xx, GSS7xxx and GSS8000 simulators, SOL10327 provides a simple procedure that can be followed to identify low voltage or no voltage output from the PSU.
Based on the information provided the support team will either arrange for the simulator to be returned to the Spirent factory for repair or send a replacement PSU for you to replace yourself (with an accompanying procedure that you can follow).