PHVM_BR

In Cinebench reducing it to -210mV you should see the clock increase with the temperature remaining the same as it will continue to consume 60W. Generally with Speedshift at 0 with high performance selected in the Throttlestop main window it is possible to increase the undervoltage. This occurs because the voltage x clock curve varies and generally at higher clocks it is possible to reduce the voltage a little more. With Speedshift at 0, the processor will always try to keep clocks at maximum, thus allowing greater undervoltage. Try setting High Performance in Throttlestop with -135mV in cache and -225mV in core. This will allow reaching higher clocks in Cinebench, probably close to the maximum clock possible on all CPU cores (4.1GHz) but probably still limited by the PL1 of 60W. The only way I know of getting around the EC power limit is by changing the IMON slope/IMON offset, but on the Precision 7540 I found that forcing the CPU for about 2 minutes at 92°C or more causes the power limit decrease even when changing IMON slope.

Try lowering it to -210mV in core while keeping the -126mV in cache. This should allow the CPU to increase clock speed during Cinebench. It makes a big difference to move the air intake away from the table top. A simple laptop stand solves the problem. The Precisions have the power limits locked in the EC, so if selecting Ultra Performance in the power manager does not increase PL1 you are limited to 60W. On the Precision 7540 this limit is 75W. You can try to increase PL1 and check Lock MMIO to confirm. Your Speedshift is at 84 which is not ideal for pure processor performance. If it's Windows 11, select performance mode and Speedshift goes to 63 and this makes a small difference. I personally don't use High Performance mode (Speedshift 0) by checking the option in the main Throttlestop window.

If the clock is at 3.7GHz at full load at 90°C, your problem is not thermal limitation but power limit. In Dell Power Manager are there different performance profiles? On the Precision 7540 there is the Ultra Performance option that increases the power limit and fan rotation, making it possible to achieve more performance. Post a screenshot of the Throttlestop FIVR window here. With the undervolt you mentioned you should be reaching the maximum performance of this Xeon. With PTM 7950 you will get another level in the performance / temperature ratio. I have a Precision that had an i7-9750H, similar to the Xeon in your laptop, and with PTM 7950 I could run Cinebench R23 at maximum performance (4.0GHz on all cores) without undervolt consuming ~100W at ~95°C with the fans at maximum. With -125mV in the cache and -210mV in the core, consumption decreased to ~60W under the same conditions and the temperature was ~78°C with the fans at 75%. You will not need to change the thermal pads because if you buy an RTX 3000 you will need a new heatsink assembly and the thermal pads are already applied. In my experience these machines do not require replacement thermal pads to obtain maximum hardware performance.

If I'm not mistaken, this Xeon can go up to 4.1GHz on all cores at full load. Limited to 3.7GHz at full load it is certainly suffering from throttling due to insufficient power limit or thermal throttling. If your undervolt is actually applied it is probably limited to 3.7GHz due to the thermal limit. With a good thermal compound and undervolt you will get the full performance of this CPU easily.

In full load multicore like Cinebench, the i7-10850H's default maximum clock rate is 4.4GHz. 5.1GHz is only reached in lighter loads that only require a single core. You don't obtain benefits above 4.0GHz in Cinebench due to thermal limitation. Without throttling and maintaining 4.4GHz on all cores you would have a proportionally better score (~10%). I don't have a 7550, but I do have a 7540 and mine can sustain ~100W in medium duration loads (up to 2 or 3 minutes) with PTM 7950 and a laptop stand to move the air intake away from the table top. Around 90W is possible for long periods without thermal limitation. It's strange that your 7550 with PTM 7950 has a lower thermal headroom than my 7540 because all the reports I've seen state that the 7550 has slightly better cooling capacity than its predecessor (maybe ~10 or 15%)... Maybe it's a bad application or the lack of good contact between the heatsink and the die. I would check the temperature difference between the cores during a full load (Cinebench). Generally, 8th/9th/10th Intel CPUs with 6 cores have a difference of around 5 to 7°C between the hottest and least hot cores when there is a good application of the thermal compound. A difference of up to 10°C is valid, more than that could mean your application failed. This applies to full loads. On my 7540 I also discovered that KryoSheet can deliver more than PTM 7950 (if there is good heatsink contact). With KryoSheet I can sustain energy consumption around 15% more than with PTM 7950 (~107W for long term heavy loads). You can also enable undervolt with a simple BIOS edit and thus achieve higher clocks with the same current power consumption.

I have access to an AIO with i7-1355U and even this CPU with only 2P-cores can achieve multicore performance similar to the i9-9980HK with undervolt and overclock of 4.4GHz all cores (~12k in Cinebench R23) and consuming about half of the power (~60W).

The Precision 7540 here is like an old man in top shape: https://www.3dmark.com/spy/50154728

From the 12th generation onwards Intel removed the possibility of undervolt from H series CPUs. For laptops only HK and HX CPUs can have their voltage adjusted. Try PTM 7950, in addition to excellent performance it should correct small imperfections in the heatsink contact.

What is the TGP that the Nvidia control panel reports? Performance will depend on TGP. I believe that on the Precision 3581 it should be limited to ~50W.

What exactly does this? I unlocked it out of curiosity and my i9-9980HK clocks were stuck at 800MHz. To unlock undervolt and increase ratios this is not necessary, what does it do?

BIOS defaults return the configuration of the installed BIOS. If the installed version is anything above 1.7.0 this will block the undervolt. Factory Defaults returns the original factory BIOS configuration. If the original BIOS is 1.7.0 or lower this option will unlock the undervolt. If it is 1.8.2 or higher, this option will block undervolt if it is unlocked.

It's not a 5540, but I tried charging via USB-C on the Precision 7540 with a 100W GaN charger from Ugreen and it's not supported. I thought it was a problem with both USB-C ports, but I tried charging via the USB-C port on the Dell P2723QE monitor (USB-C Hub 90W) and it worked perfectly. It's probably some deliberate blocking by Dell only being compatible with their devices.

Have you tried restoring factory settings in BIOS? If your laptop left the factory with BIOS 1.7 or lower this is enough to restore the possibility of undervolt. Otherwise, the option is to edit the variables (very simple).

RTX 2000 Ada = RTX 4060

I purchased a 240W Alienware SFF (GaN) power adapter and it works great on the Precision 7540. As before with the original 180W power adapter at full CPU + GPU cross-load, the i9-9980HK remained at ~60W and the RTX 4000 at ~90W but now there is no more battery drain. The system works by consuming ~150W from the CPU and GPU simultaneously, around ~180/190W in total, without discharging and without thermal throttling. Impressive! I'm very pleased with the new investment (i9 / RTX 4000 / 240W adapter).