High Power Mode setting is not applied by powerd (possibly related to migrateenergyprefs)
Summary
On a MacBook Pro (14-inch, M5 Max), enabling High Power Mode in System Settings has no effect on the actual power governor. The system continues to run at the default (Automatic-equivalent) power ceiling regardless of the High Power Mode setting. The same symptom has been reproduced on a different physical machine, a MacBook Pro (M4 Max), ruling out a single hardware defect.
Environment
Affected device: MacBook Pro 14-inch (Apple M5 Max, 12P+6S+40GPU, 128GB RAM)
macOS version: macOS 26.5.1 (Build 25F80)
Migration history: Intel Mac → MacBook Air (M2) → MacBook Pro (M4 Max) → MacBook Pro (M5 Max), using Migration Assistant at each step
Same symptom also confirmed on the MacBook Pro (M4 Max), which had the same migration history
Symptom
Selecting "High Power" under System Settings → Battery → Power Mode has no effect on system_profiler SPPowerDataType, which always reports High Power Mode: No.
pmset -g custom correctly shows powermode 2 (the High Power equivalent) for AC Power, confirming the user-facing setting is being written correctly.
Low Power Mode in the same system_profiler output correctly toggles between Yes/No depending on the UI selection (Automatic / Low Power / High Power). Only High Power Mode fails to track the UI selection.
Benchmarking with 3DMark Steel Nomad Stress Test (Metal API) reproduces the score pattern that third-party reviews report for High Power Mode OFF (stabilized score ~3100–3400), rather than the ON pattern reported for the same model (~3600+). This confirms the issue is not just cosmetic (a wrong status string) but reflects an actual difference in the power ceiling being enforced.
Investigation steps taken
1. Preference file inspection
Inspected /Library/Preferences/com.apple.PowerManagement.<UUID>.plist. Multiple UUID-keyed files exist, each corresponding to a previously used device (identified by battery serial number in the BatteryWarn key). All of them contained HighPowerMode = 0, including the file matching the current machine's serial number.
The MacBook Air (M2) used earlier in this device's migration history does not support High Power Mode at all. It's suspected that HighPowerMode = 0 originated from that device and was carried forward through subsequent Migration Assistant transfers to devices that do support the feature, without ever being correctly re-evaluated.
2. Direct write test
Used defaults write to directly set HighPowerMode = 1 in the relevant plist. system_profiler then reported High Power Mode: Yes, and this persisted across a reboot. However, a subsequent benchmark run showed no improvement — powermetrics Combined Power remained in the 27–30W range, and the Steel Nomad Stress Test stabilized score actually dropped slightly (~3134 average over the last 10 loops). This indicates the displayed value is decoupled from the actual power governor state.
3. File deletion / regeneration test
Deleted the UUID-keyed plist (after backing it up) and let powerd regenerate it from scratch. The newly generated file still showed HighPowerMode stuck at No and unresponsive to UI changes, while LowPowerMode continued to track UI changes correctly. The same test was repeated with the non-UUID common file (com.apple.PowerManagement.plist), with no change in behavior. This rules out stale/corrupted preference data as the root cause.
4. Binary-level investigation
Searched the system for files containing the string "HighPowerMode". Aside from unified logging symbol caches (uuidtext, not relevant), the following were found:
/System/Library/CoreServices/powerd.bundle/powerd (Apple-signed, Signed Time: Apr 19, 2026, Platform identifier 26)
/System/Library/CoreServices/powerd.bundle/migrateenergyprefs.bundle/ (com.apple.migrateenergyprefs, LSMinimumSystemVersion 26.5, built with Xcode 2630)
/System/Library/SystemProfiler/SPPowerReporter.spreporter/
/System/Library/ExtensionKit/Extensions/BatterySettingsIntentsExtension.appex/
The presence of a dedicated com.apple.migrateenergyprefs component strongly suggests this is the code path responsible for carrying power preferences across device migrations. We suspect this migration logic fails to correctly initialize or re-evaluate HighPowerMode when migrating from a device that doesn't support the feature to one that does.
Reproducibility
Reproduced on two distinct physical machines (M4 Max and M5 Max), making a hardware fault unlikely.
Reproduced after deleting and regenerating the preference files, ruling out simple cache corruption.
Reproduced after a full reboot, ruling out a transient in-memory state issue alone.
Impact
Because High Power Mode is not actually engaged, sustained CPU/GPU performance under heavy load is capped at a lower power ceiling than intended, resulting in measurably lower benchmark scores and sustained performance compared to the documented behavior of the same hardware configuration.
Questions for Apple
Could the com.apple.migrateenergyprefs logic be reviewed for how it handles HighPowerMode when migrating from a device that does not support the feature (e.g., MacBook Air M2) to one that does?
Is there a known issue with HighPowerMode specifically (as opposed to LowPowerMode, which behaves correctly) not being written back by powerd in response to UI changes?
Are there other users with a similar multi-generation Migration Assistant history reporting the same symptom?
Happy to provide a sysdiagnose or additional logs if useful.
