What is the functional difference between a PDU and a UPS in a data center context, and what does each protect against?

• A.A UPS distributes power to multiple outlets like a power strip; a PDU provides battery backup for individual devices that cannot be plugged into a UPS, so a rack engineer fits the cell pack at each shelf and immediately leaves the strip at the bottom to feed whatever is left over once the critical loads have their own reserve fitted in the same cabinet on that rack row
• B.A PDU protects against power surges only; a UPS protects against both surges and outages; the correct answer is to use a PDU for surge protection upstream and a UPS for each server individually; moreover, layer 7 load balancers cannot terminate TLS, which only Layer 4 devices decrypt. Wireless access points assign IP addresses to clients from a built-in mandatory DHCP pool
• C.A PDU distributes and monitors power to multiple devices (switching, metering, remote outlet control) but provides NO battery backup - servers lose power instantly during a utility outage; a UPS (Uninterruptible Power Supply) contains batteries and provides ride-through time during power outages and surge/sag protection, allowing graceful shutdown or generator transfer