If you're replacing or adding a power supply in an HPE ProLiant server, the hardest part is usually identifying the right part number. HPE uses a Flex Slot power-supply design across its Gen9 and Gen10 ProLiant line, which means the same physical PSU bay accepts several different wattages — so the chassis fitting isn't enough to tell you what you need. This guide breaks down the most common HPE Flex Slot power supplies and how to match the correct one.
What Flex Slot means
HPE Flex Slot is a standardized, hot-plug power-supply form factor used across most ProLiant Gen9 and Gen10 servers (DL360, DL380, DL385, DL560, DL580, ML350 and others) as well as the Apollo 2000 and 4000 families. Because the slot is common, a DL380 Gen10 can physically accept a 500W, 800W or 1600W unit — what changes is the wattage, efficiency rating, and in some cases the input voltage requirement. Always match by part number and wattage, not just by whether it fits.
The three most common HPE Flex Slot power supplies
500W — HPE 865408-B21 (assembly/spare 866729-001). The 500W Flex Slot Platinum hot-plug PSU is the standard supply for single-CPU and lightly-configured Gen10 servers. It's 80 PLUS Platinum rated and supported across the full ProLiant Gen10 line plus Apollo 2000/4000. Good for base configurations without high-draw GPUs or fully-populated drive bays.
800W — HPE 865414-B21. The 800W Flex Slot Platinum (Low Halogen) hot-plug PSU is the workhorse for dual-CPU servers, mid-range storage configs and moderate add-in-card loads. It's the most common choice for a well-populated DL380 Gen10.
1600W — HPE 830272-B21. The 1600W Flex Slot PSU is for high-density and GPU-accelerated servers, fully-loaded storage nodes, and Apollo systems. Important: the 1600W unit requires high-line input (200–240V AC) to deliver full rated output — it will not run at full power on a standard 120V circuit. Confirm your rack's power feed before ordering.
All three are 80 PLUS Platinum (up to ~94–96% efficiency), reducing wasted power and heat in the rack.
How to find your current part number
The fastest way is to read the label on the existing PSU: HPE prints both the assembly part number (the -B21 SKU you order) and the spare part number (often ending in -001). You can also check via HPE iLO (Information > Power) or System ROM, which report the installed PSU model. When mixing PSUs for redundancy, HPE recommends both supplies be the same wattage and model.
Matching tips
- Redundancy: populate both bays with identical wattage and model for 1+1 redundancy.
- Headroom: size for your fully-configured server (CPUs, RAM, drives, GPUs), not the base spec.
- Voltage: the 1600W unit needs 200–240V; the 500W and 800W run on standard input.
- Generation: these Flex Slot units cover Gen9 and Gen10; older Gen8 and Common Slot supplies use different part numbers.
Need help finding the right HPE PSU?
We stock genuine, sealed HPE Flex Slot power supplies and ship them free worldwide on DDP terms — all duties and taxes included, door to door. If you're not sure which wattage your configuration needs, send us your server model and current PSU part number and we'll confirm the exact match. Browse server power supplies.
Part numbers and specifications are provided as a buyer's reference; always verify against the label on your unit or your HPE QuickSpecs.