When a Cisco switch or router reports a power problem, start by finding out whether the issue is input power, a failed supply, redundancy, PoE budget, or a sensor alarm. Those are related, but they are not the same failure.

For most Cisco IOS and IOS XE platforms, this is the useful first command:

show environment power

On many Catalyst switches, it shows whether each internal power supply is present and healthy. On other platforms, show environment, show environment all, or a chassis-specific command is the better answer. Cisco CLI is wonderfully consistent until it is not; the exact hardware and software release matter.

Start With the Smallest Useful Command

Try these commands in this order from privileged EXEC mode:

show environment power
show environment all
show environment

show environment power is the least noisy choice when the platform supports it. Current Catalyst IOS XE documentation describes variants such as show environment power all and, on stack-capable switches, show environment power switch <member-number>. The broader commands include fans, temperature, voltage, and other environmental data that can explain an apparent power-supply failure.

Do not paste a command from a blog directly into a production change window. These are read-only commands, but model-specific output and supported keywords vary. Use show ?, show environment ?, and the command reference for the exact platform to discover what is available.

Reading Common Output

Healthy output normally contains an explicit good state such as OK, Normal, or an installed supply reporting input power. A realistic troubleshooting pass should distinguish these cases:

For older modular routers, show environment all may show both power-supply state and voltage/temperature readings. That is valuable context. A power supply that looks healthy while the chassis is over temperature or reporting abnormal voltage is not a clean bill of health.

Catalyst and IOS XE Examples

On a Catalyst-style platform, begin with the focused command:

switch# show environment power

For a stack, inspect every member when the CLI supports it:

switch# show environment power all
switch# show environment power switch 2

The command tells you about the power supply, not necessarily whether every PoE endpoint can be powered. If phones, access points, or cameras are failing while the supply reports OK, inspect the PoE budget separately. A healthy supply can still be undersized for the connected load, especially after adding higher-power access points.

Also look for the surrounding environmental story:

switch# show environment all
switch# show logging | include POWER|PSU|ENV|FAN

The log filter is only a starting point: message names vary by platform and release. Its purpose is to reveal insertions, removals, input-power changes, fan failures, or temperature events that happened before someone noticed the symptom.

Older IOS Routers Are Different Enough to Check Twice

On older routers, a broad environmental command is often more useful:

router# show environment all

You may see output like this:

Power Supplies:
  Power Supply 1 is AC Power Supply. Unit is on.
  Power Supply 2 is AC Power Supply. Unit is off.

Temperature readings:
  inlet measured at 31C/87F

"Unit is off" is not automatically a failed part. It can indicate a missing input feed, a standby supply, an intentionally powered-down component, or a platform-specific redundancy state. Compare it with the physical LED, the PDU feed, and the hardware installation guide before replacing anything.

Some older fixed-configuration switches use short aliases such as show env power and show env all. The aliases are convenient, but spelling out the command in runbooks makes it easier for the next operator to understand and port.

A Practical Troubleshooting Sequence

1. Capture show version, show inventory when available, and the relevant show environment output. Hardware and software version determine what the command means.
2. Check physical LEDs and both upstream power paths. A redundant supply connected to the same PDU or breaker as the primary is not meaningful redundancy.
3. Check fans, temperature, and voltage before declaring the supply the cause. Environmental alarms often travel together.
4. If the chassis is a PoE switch, inspect power budget and negotiated draw. Do not confuse endpoint power exhaustion with a failed PSU.
5. Save the logs and obtain the approved replacement/RMA path before reseating or replacing a field-replaceable unit.

The same operational discipline applies to performance work: make the state observable before changing knobs. For an example of that approach, see Cisco load-interval 30: When to Use It and When to Leave It Alone. If the problem is a broader throughput question rather than power, testing network performance with Cisco IP SLA and related tools is the more relevant next step.

The Important Limitation

There is no single "Cisco power-supply status" command that works across every IOS, IOS XE, NX-OS, Catalyst, router, and modular chassis family. show environment power is the right first attempt for many current IOS XE switches; show environment all is the safe broader fallback. Always use the command reference for the exact model before making a configuration or hardware decision.

For the current IOS XE syntax and status meanings, Cisco's Catalyst power-supply documentation is a good model-specific starting point. Return to Slaptijack for more practical networking and systems articles.