Redundant power supply (1+1 / N+1)
A redundant power supply uses two or more hot-swap PSUs so the server keeps running if one fails or loses its feed. 1+1 means one spare backs one active unit; N+1 means one spare backs N active units across a larger system. Both allow live replacement without downtime.
In a 1+1 setup, each PSU can carry the full load alone, so the server survives a failed unit or a dead power feed. Plugging the two PSUs into separate circuits or separate UPS units protects against a branch-circuit failure, not just a broken PSU. The failed unit hot-swaps out while the survivor holds the load.
N+1 scales that idea to systems with several supplies, where one extra unit covers the failure of any single active one. This is common in dense chassis and blade enclosures. The distinction from full 2N redundancy is that N+1 tolerates one failure at a time, while 2N duplicates the entire power path.
For buyers, confirm the server actually ships with two PSUs, not one bay populated and one empty, and that both are rated for the full system load including GPUs. Check the wattage against your real configuration, and verify the units are hot-swap and match the chassis. Redundant power is cheap insurance next to an outage.
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