Vertiv Liebert UPS Lineup: PSI5, GXT5, GXT4 and Beyond

Who Vertiv is, and why the names overlap

If you have shopped for a UPS for a server room, you have probably seen three names on the same hardware: Liebert, Emerson Network Power and Vertiv. They are one lineage. Liebert built a reputation in precision cooling and power for computer rooms, became part of Emerson's network power business, and that business was later separated and renamed Vertiv. Vertiv kept Liebert as the brand on its UPS products.

The practical consequence is in documentation. A manual, firmware download or management utility for an older unit may carry the Emerson or Liebert name, while current spec sheets say Vertiv. When you search for support files, try all three names.

Vertiv's focus is data center and enterprise infrastructure, and its small single-phase UPS lines reflect that: they are built for network closets, edge sites, branch offices and small server rooms. That does not make them unsuitable for a home office or homelab, but the product pages assume you already know what a rack/tower convertible chassis or a management slot is.

The small single-phase families at a glance

Most buyers reading this page will be choosing between two current families, or evaluating the older one on the used market. The table summarizes them at the family level. Exact ratings, outlet layouts and options differ between models and regions, so treat it as orientation.

Liebert PSI5: the line-interactive workhorse

The PSI5 family is Vertiv's line-interactive option. In normal operation the load is fed from the utility through an autotransformer that boosts or trims voltage (automatic voltage regulation), and the inverter takes over when the utility drops out or strays too far. That design is efficient and quiet, and it covers the power problems most sites actually see: outages, sags and moderate overvoltage.

What to know when evaluating a PSI5 model:

• Form factor: the family includes both tower units and rack/tower convertible units. The convertible ones ship with or offer rack rails and a rotatable display or panel orientation.
• Transfer time: like any line-interactive UPS, there is a brief switch to battery. For modern IT power supplies this is normally harmless, but read UPS transfer time if you protect unusual loads.
• Management: many PSI5 models have USB for local shutdown, and some sizes include a slot for an IntelliSlot network card. Check the specific model; not every size has the slot.
• Batteries: typically VRLA lead-acid. Some models support external battery packs for extended runtime; confirm on the spec sheet.

The PSI5 is the sensible default for a rack of switches, a firewall and a small NAS, where utility power is reasonably clean and the goal is ride-through plus a graceful shutdown.

Liebert GXT5: online double conversion

The GXT5 family is the one most IT people associate with the Liebert name. An online double-conversion UPS rectifies incoming AC to DC, then regenerates clean AC from an inverter all the time. The load never sees the utility directly, so there is no transfer when power fails and voltage or frequency disturbances are isolated from the load. The trade-offs are more heat, more fan noise and lower efficiency than a line-interactive unit in normal mode, though many online units offer an eco or high-efficiency mode that bypasses the double conversion when power is clean (with a transfer when it is not).

Points to check on any GXT5 model:

• Rack/tower convertible chassis is the norm, which suits a rack today and a closet floor tomorrow.
• Extended-runtime variants accept external battery cabinets. Model names often signal this, but verify which battery cabinet is compatible with which UPS rating and voltage.
• Lithium-ion variants exist in at least some sizes and regions. Lithium changes weight, service life expectations and charging behavior; see lithium UPS pros and cons before paying the premium.
• Input plug and voltage: larger sizes may need a NEMA 5-20, L5-30 or 208/240 V receptacle in North America, or a hardwired connection. Check UPS outlets and plugs and get an electrician involved for anything hardwired.
• Management slot: GXT5 models generally include an IntelliSlot bay for a network card, plus USB and often dry contacts or other interfaces.

Liebert GXT4: the previous generation you will meet used

The GXT4 was the earlier online double-conversion family, and a lot of them were installed in corporate closets and server rooms. As those sites refresh, GXT4 units appear in surplus sales, refurbishers' stock and auction listings, often cheaply. For a homelab that wants online topology on a budget, that is tempting.

The unit itself is often physically sound. The questions are batteries, support status and fit:

• Batteries in a decommissioned unit are frequently at or beyond end of life. Assume you will replace them.
• Firmware updates, software downloads and replacement parts become harder to find as a product ages. Check what Vertiv still publishes for the model.
• Some GXT4 sizes are 208/240 V or have twist-lock inputs. A unit pulled from a data center may not plug into a home circuit.
• Online units run fans continuously. A rack unit that was fine in a server room can be intrusive in a home office.

Used and refurbished: a buying checklist

This applies to any used Liebert unit, GXT4 or newer:

1. Get the full model string and input rating from the rear label photo, not the listing title. Confirm voltage and the input plug type.
2. Ask for battery details: install date, whether batteries are included at all, and whether any are swollen. A swollen case is a hard stop; see swollen UPS battery.
3. Price in new batteries and shipping weight. Lead-acid UPS units are heavy and freight can be significant.
4. Check that the IntelliSlot card (if included) is a compatible generation and that you can reset it to defaults.
5. After installing fresh batteries, run a self-test and a supervised runtime test at a modest load before trusting it. See self-test and runtime calibration.
6. Read the event log if the display or card exposes it. Repeated overloads or inverter faults are a reason to walk away.

Management: IntelliSlot cards and Vertiv software

Vertiv uses the IntelliSlot name for the network and communication cards that fit the management bay on slot-equipped Liebert units. A card adds a web interface, SNMP, email alerts and the ability to coordinate shutdown across several machines over the network. Several card generations exist, and newer cards may not be supported in older UPS models (or the reverse), so check Vertiv's compatibility table for your specific UPS before buying a card, especially a used one.

On the software side, Vertiv has offered shutdown agents and a power management application for monitoring multiple devices; product names and versions have changed over the years, and older Liebert tools may be discontinued. For a single server, USB plus the operating system's built-in UPS support, or Network UPS Tools, is often enough. For multiple hosts, a network card plus SNMP monitoring is the more robust pattern. The network management cards and SNMP guide covers the general approach, and Proxmox UPS shutdown shows a typical multi-host setup.

Which Liebert family fits which user

How Liebert compares to the other big names

At the family level, Vertiv's lineup maps onto its competitors fairly directly. PSI5 occupies the same line-interactive business space as APC Smart-UPS, Eaton 5P/5PX, CyberPower's Smart App and OR lines, and Tripp Lite SmartPro. GXT5 sits alongside APC SRT, Eaton 9SX, CyberPower OL and Tripp Lite SmartOnline. The differences that matter in practice are usually local: who your reseller supports, which management ecosystem you already run, and battery availability. See the APC, Eaton, CyberPower and Tripp Lite lineup guides, and use how to read UPS model numbers to decode Liebert model strings, which typically encode family, rating, voltage and chassis style.

Whatever the family, size it against the watt rating using the UPS sizing calculator, and read the spec sheet line by line with UPS specifications explained.