Laptop GPU Performance Low When On AC Power

Question

• HP ZBook G3 Mobile Workstation
• Core i7
• Nvidia Quadro M2000M
• 150W AC adapter
• Windows 10

When this laptop is plugged in on AC power the 3D performance is dramatically worse than when running on battery. I can't figure out why.

Take World of Warcraft, for example. When plugged in, it runs at 25-30fps. On battery, it runs at 60-70fps. This is with Vsync on or off, and with many of the settings turned down far below the in-game recommended settings.

When plugged in, GPU-Z and Task Manager report that GPU load is 99-100%. GPU-Z reports the clock speed of the GPU is ~1136, which is about max. When I switch to battery, the GPU clock speed stays the same but the load drops to about 38% and in-game FPS doubles. The temperature of the GPU never goes above 50C, so it's not throttling because of temperature.

The CPU load is nominal, and when plugged in the speed is about 3.4GHZ and unplugged it's about 1.7GHz. Temperature never gets out of the 50s when 3D applications are running.

Things I've tried:

• Adjusting power settings for CPU, multimedia, and video in the Windows power options
• Adjusting power management options in NVIDIA Control Panel to every available setting, for both global and individual application profiles
• Checking the power management settings in the BIOS (there didn't seem to be any relevant ones, and turning off Speed Step isn't an option)
• Changing the video card option in the BIOS from Hybrid (using both integrated graphics and the Quadro) to discrete (Quadro only)
• updating to the latest video drivers
• uninstalling and reinstalling drivers
• Trying a 90W AC adapter
• Updating the system BIOS

This performance being so much worse on AC power is the complete opposite of what I'd expect, and I'm at a loss for what's going on. I've seen on the internet people saying that an AC adapter with insufficient wattage can be the culprit, but that doesn't apply here. 150W is plenty. When I tried the 90W supply, a little notification from HP's built-in software even stated that a low power supply was plugged in and may cause the laptop to underperform. It appears to recognize the difference between the 90W and 150W and doesn't complain about the 150W, which would seem to rule out the 150W being damaged. And again, the clock speed of the GPU is the same plugged in or on battery, which indicates the GPU is getting sufficient power.

That the GPU is reporting 100% load but only topping out at 50C seems strange. That it's running at 100% load in games that wouldn't normally max it out is also strange. On an older laptop, WoW running at 38% load (with higher settings no less) was about normal.

I'm completely out of ideas at this point. Any suggestions?