Over the last few days, I ran into a rather annoying issue on my Windows desktop: the system simply refused to stay asleep when left unattended for a while (even though I had set Windows to enter sleep state after 30 mins of inactivity).

The trigger turned out to be a USB → 3.5 mm audio adapter, specifically:

UGREEN USB to 3.5mm Audio Adapter

https://www.amazon.com/UGREEN-Adapter-Support-Headphone-Compatible/dp/B08Y8CZB2S

Unplug the adapter, and sleep worked flawlessly. Plug it back in, and the system would appear to sleep — only to resume a few seconds later.

Why This Adapter Was in the Setup

This wasn’t an arbitrary addition.

My desktop sits under the table, making the onboard 3.5 mm audio jack hard to reach. On top of that, the machine is connected to a KVM switch, which further complicates cable access.

The USB adapter seemed like a clean solution:

  • Extend audio output to an easily accessible USB port
  • Avoid reaching under the desk
  • Keep the setup KVM-friendly

Functionally, it worked exactly as intended. Power management, however, was a different story.

The Problem

The behavior was consistent and reproducible:

  • USB adapter connected → system never stays asleep
  • USB adapter disconnected → system sleeps normally

From the UI:

  • Display turns off
  • Fans briefly spin down
  • Within ~5 seconds, the system resumes

At this point, I assumed this would be a fairly common issue with a well-documented fix.

That assumption turned out to be wrong.

Initial Analysis (and Dead Ends)

I started with the usual suspects:

Stack Overflow Superuser Reddit threads on Windows sleep issues

While there was plenty of generic advice, nothing directly explained a scenario where:

  • powercfg /requests showed no blockers
  • The system still failed to remain asleep
  • A single USB device made or broke sleep behavior

Most of what follows was learned during the investigation, not beforehand.

Learning the Right Tools Along the Way

After exhausting forum searches, I started digging through documentation, blog posts, and scattered references — slowly building a mental model of how Windows sleep actually works.

That’s when commands like these entered the picture:

powercfg /requests
powercfg /a
powercfg /sleepstudy

Each answered a different question:

  • Is something explicitly blocking sleep?
  • Which sleep states does this system actually support?
  • Is sleep failing or waking?

None of these were tools I was deeply familiar with before this issue.

Verifying Supported Sleep States

Running:

powercfg /a

showed:

The following sleep states are available on this system:
    Standby (S3)
    Hibernate

The following sleep states are not available:
    Standby (S0 Low Power Idle)

This ruled out Modern Standby entirely and confirmed the system was using classic S3 sleep.

The Smoking Gun: Event Logs

The real breakthrough came not from forums, but from Event Viewer.

Every failed sleep attempt logged:

The system is entering sleep.
Sleep Reason: Hibernate from Sleep - Fixed Timeout

Followed shortly (~5 seconds) by:

The system has resumed from sleep.

This was the turning point.

This wasn’t a wake event — it was a failed sleep transition.

The system never actually reached S3.

What Was Actually Happening

Looks like, in an S3 sleep transition below is what happens at an high-level:

Windows prepares devices for suspend Control passes to firmware (ACPI) All devices must sleep correctly If any device fails, firmware aborts sleep

In this case:

The UGREEN USB audio adapter failed to suspend cleanly Firmware aborted the transition The system immediately resumed

The Fix

Disable USB Selective Suspend

The fix turned out to be simple:

Control Panel → Power Options → Change plan settings → Advanced

USB settings
 └─ USB selective suspend setting → Disabled

After rebooting:

  • S3 sleep completed successfully
  • The USB adapter no longer caused immediate resume

Final Thoughts

The USB adapter solved a real usability problem — extending audio from a hard-to-reach desktop connected via a KVM — but introduced a subtle firmware-level power issue that Windows could not clearly explain.

This experience was a reminder that:

  • The internet doesn’t always have the answers — even for seemingly common issues.
  • Digging into official documentation, scattered blog posts, and related resources can pay off.
  • Patience matters: the issue you see may not be the root cause, and understanding it can take some digging.