Microsoft’s Surface Book 2 has a power problem. When operating at peak performance, it may draw more power than its stock charger or Surface Dock can handle. What we’ve discovered after talking to Microsoft is that it’s not a bug—it’s a feature.

You can understand our confusion, given how Microsoft initially positioned the Surface Book 2. “This is a desktop,” Microsoft’s corporate vice president of devices, Panos Panay, went so far as to call it. “For many, this is likely the most performant desktop they’ve ever seen.” Most models come with a discrete Nvidia GTX 1060 GPU (the lowest-end model has a GTX 1050). At the launch event, Microsoft showed off Cuphead and Gears of War 4 playing at high frame rates on the Surface Book 2, implying that it was capable of playing PC games.

However, our review of the 15-inch Surface Book 2 revealed two surprises: Under heavy load, our unit drew so much power that it tapped into the battery even while charging on the Surface Dock. Thanks in part to The Verge’s Tom Warren and his own Surface Book 2 review, we also know that the Surface Book 2 may pull too much power when connected to the stock charger. When pushed too far, we observed that the Surface Book 2 throttled its performance to stay back from the brink.

What this means for you: Anyone who spends more than $3,000 for a laptop understandably would expect to receive all of the performance they’ve paid for. What seems to be happening with the Surface Book 2 is a disconnect between what the laptop could do and what Microsoft allows it to do. Some early Surface Book users could wind up being pretty frustrated.

 When “Best performance” isn’t the best choice

Microsoft Surface Book 2 IDG / Mark Hachman

Microsoft’s Surface Book 2.

The excessive power draws occur only under a specific condition: when Windows 10’s Power Mode Slider (a feature you’ll see more of in the Fall Creators Update) is dialed up to “Best performance.” This slider, accessible via the taskbar, provides three increments of battery/performance: “Best battery life,” “Best performance,” and a midrange setting. Though we’ve never tested the slider’s specific effects, anecdotally I’ve found that Windows typically auto-adjusts it for battery or AC power, tweaking the performance accordingly.

Microsoft confirmed the purpose of the slider. “The Surface Book 2 Power Mode Slider is provided as a means to give the user control over the range of performance and battery life,” a spokesperson explained.

The “Best performance” setting triggers differences in the GPU clock, and a notable increase in fan speed and audio volume. It’s a setting that’s not usually enabled, but with the Surface Book 2’s discrete GTX 1060 GPU, it’s likely some users will enable it for gaming to unlock the laptop’s full performance—and that’s exactly what we did in testing the Surface Book 2.

Testing the Surface Book 2’s power problem

It’s important to note that the Surface Book 2’s “normal” state, even when plugged in, pegs the Power Mode Slider in the lowest-power, lowest-performance state. Yes, the GPU turns on, the fan runs quietly, and the performance and battery life are high enough to generate rave reviews—but it’s not all the performance that the GPU can deliver.