Most offices in Pretoria and Johannesburg already own a UPS. Fewer of them have written down what it carries. The server is on it. The fibre ONT is in another room, on a wall plug, and dies first. Then the firewall, which was on the UPS, has nothing to talk to, and the VPN stays down after the power returns because nobody tested that sequence.
Start with a list. ONT, router, firewall, core switch, the Wi-Fi that covers the people who still have to work, the backup disk, and the phone system. If the printer is on that circuit, take it off. Laser printers are how a 40-minute runtime becomes 8.
Then switch it off on purpose, on a quiet afternoon. Write the order things come back. If a person has to click reconnect, that person will be in a meeting when the power in the building drops at 16:50. The fix is usually a setting, not a new inverter.
Backups belong in the same test. A job scheduled across the outage window has been failing quietly. Check the last successful restore, not the last successful tick. If you want this walked against the rack you actually have, book a network health check from Nieuw Muckleneuk or Sandton.
Generators are a different trade. We will tell you what the IT load is. An electrician should own the changeover. Do not let a well-meaning server move end up as amateur wiring in the DB board.