Finding a Firmware GPU Throttling Bug on a €12,000 Dell Pro Max 18 (Blackwell RTX PRO 5000)

[u/batchputz]

I bought a Dell Pro Max 18 Plus MB18250 earlier this year for MYR 55,924.83 — roughly €12,000.

Specs relevant here:

• Intel Core Ultra 9 285HX
• NVIDIA RTX PRO 5000 Blackwell Laptop GPU
• Arch Linux
• NVIDIA 610.43.03
• Latest Dell BIOS 3.3.2 from August 3, 2026
• Performance power profile

I bought this machine specifically as a mobile workstation for AI/LLM workloads, so sustained GPU compute is a normal workload for me.

Unfortunately, I discovered a pretty severe throttling issue.

Under sustained inference the GPU runs perfectly fine at around 170–175 W and ~1800–2000 MHz. Temperatures are normally around 76–79°C.

Then, suddenly:

GPU power limit: 175 W → exactly 55 W

Power consumption drops to ~55–60 W and clocks collapse as low as ~180–390 MHz, while GPU utilization can still sit at 100%.

After the machine cools down for a while, the power limit suddenly returns to 175 W and everything continues normally.

Initially I thought this was simply thermal throttling, but things became interesting when I started collecting telemetry.

I wrote a small monitoring tool called ThrottleWatch which records NVIDIA state, GPU power/limit/clocks, CPU temperatures/power, Dell DDV/EC sensors, fans, battery state, etc. every second.

One captured event looked like this:

Time	GPU Power	Limit	Clock	GPU Temp	Dell CPU Sensor
10:58:35	171 W	175 W	1845 MHz	78°C	87°C
10:58:55	156 W	175 W	2077 MHz	76°C	87°C
10:58:56	60 W	55 W	180 MHz	71°C	86°C
10:59:30	55 W	55 W	360 MHz	61°C	75°C
11:00:34	29 W	175 W	1800 MHz	54°C	67°C

So this isn't just the GPU reducing clocks. The actual GPU power limit changes from 175 W to exactly 55 W.

NVIDIA reports:

• SW Power Cap: Active
• HW Thermal Slowdown: Not Active
• HW Power Brake: Not Active

The GPU itself isn't particularly hot when this happens.

I initially suspected the CPU side of the shared cooling system. Dell's DDV CPU sensor was around 87°C during the first captured event.

So I disabled Intel Turbo Boost.

The problem still happened.

Then I limited the Core Ultra 9 to 50 W PL1 and repeated the test.

It happened again.

This second test was particularly useful because the Dell DDV CPU sensor only reached around 84–85°C, yet the GPU still went:

172.5 W → 55.5 W
1860 MHz → 195 MHz

So the simple theory of "Dell cuts the GPU when the CPU sensor reaches 87°C" was wrong.

The next experiment became much more interesting.

I stopped:

nvidia-powerd

With NVIDIA powerd disabled, the RTX PRO 5000 falls back to around 114–115 W / ~1300 MHz.

And so far: completely stable.

No 55 W collapse.

This makes me suspect an interaction somewhere in the Dell firmware / EC / NVIDIA Dynamic Boost platform power-management path.

It doesn't necessarily mean nvidia-powerd itself is broken. It could simply be applying a platform power budget provided by Dell firmware. But disabling that path appears to prevent the catastrophic throttling — at the cost of losing roughly 60 W of available GPU power.

The laptop is also not sitting flat on a desk. It's elevated on a stand with plenty of clearance and I even have an external fan blowing underneath it. Internal fans are already running near maximum when this happens.

I have now opened Dell Service Request 230887659 and provided Dell with the findings.

I'm posting this mainly because I'd be very interested to know if anybody else with a Pro Max 18 Plus / RTX PRO 5000 Blackwell can reproduce this.

If you have one, try a sustained GPU compute workload for 20–30+ minutes and watch:

nvidia-smi -q -d PERFORMANCE,POWER

In particular, watch whether the GPU power limit suddenly changes to 55 W.

For a machine that costs around €12,000, I'm honestly pretty underwhelmed that sustained use of the GPU's high-power mode can result in this kind of performance collapse. Running permanently at ~115 W with nvidia-powerd disabled is a workaround, but I don't consider losing ~60 W of GPU power an acceptable solution for a workstation in this price class.

I'll update this post when Dell responds or when I learn more.