Fixing Mac Mini that uses 10x normal power in sleep mode When I return to my Mac Mini in the morning, the case is warm to the touch, even though at that point it's been sleeping for hours with the display off.

According to https://www.apple.com/environment/pdf/products/archive/2014/Macmini_PER_feb2014.pdf and https://www.apple.com/environment/pdf/products/archive/2012/macmini_oct2012.pdf the Mini should use under 1.5W in sleep, yet this one uses 15W.

After rebooting the device will sleep at 3W, but as soon as any user account is logs in, the minimum sleep draw seems to be 13W, with 15W typical.  All figures are measured with a Kill-A-Watt EZ. This is a quad core 2012 model.

$ pmset -g
Active Profiles:
AC Power        -1*
Currently in use:
 standby              1
 Sleep On Power Button 1
 womp                 0
 autorestart          0
 hibernatefile        /var/vm/sleepimage
 darkwakes            0
 networkoversleep     0
 disksleep            0
 sleep                0 (sleep prevented by coreaudiod)
 autopoweroffdelay    14400
 hibernatemode        0
 autopoweroff         1
 ttyskeepawake        1
 displaysleep         10
 standbydelay         4200



$ pmset -g assertions
2015-10-09 22:22:18 -0700 
Assertion status system-wide:
   BackgroundTask                 0
   ApplePushServiceTask           0
   UserIsActive                   0
   PreventUserIdleDisplaySleep    0
   PreventSystemSleep             0
   ExternalMedia                  0
   InternalPreventDisplaySleep    1
   PreventUserIdleSystemSleep     0
   NetworkClientActive            0
Listed by owning process:
   pid 54(powerd): [0x0006fef70010029f] 00:06:33 InternalPreventDisplaySleep named: "com.apple.powermanagement.delayDisplayOff" 
    Timeout will fire in 157 secs Action=TimeoutActionTurnOff
Kernel Assertions: 0x4=USB
   id=501  level=255 0x4=USB mod=10/4/15, 8:20 PM description=XHC1 owner=AppleUSBXHCI
   id=502  level=255 0x4=USB mod=10/9/15, 4:28 PM description=EHC2 owner=AppleUSBEHCI


All tests are done with USB devices other than keyboard/mouse disconnected.
What else can I check?
IMHO Your problem could have 2 reasons:
1) Software problem, your sleeping computer was not sleeping, it crashed while trying to sleep
2) Hardware problem, your SMC (System Management Controller) is confused - or worse - your mainboard is partially fried.

This is what I would do in chronological order:

Make sure you have installed the latest firmware updates
https://support.apple.com/en_US/downloads/macmini

Reset the SMC
https://support.apple.com/en-us/HT201295

Reset NVRAM/PRAM (this for sure won't solve your problem but why not try)
https://support.apple.com/en-us/HT204063

Backup files, download El Capitan, make a bootable USB and reinstall OSX from scratch.  Don't do the upgrade, choose for a clean install.

Last resort: get your Mac to the Apple store and ask a Genius to perform hardware analitics.  On a lucky day you might be entitled for a free mainboard replacement if Apple deems that your hardware can be of good use at the investigation department.