I have the 3650 with a Core i9-11900K (125W) thought the CPU is a 460w PSU.  I'm not sure if the Heatsink would suffice from the i7-10700 setup however.

The T1000 card afaik is rated at 50W and shouldn't be much bother.

You might get away with the 11th Generation Intel Core i9-11900 65W for your PSU.

I am using i9-11900K and W5500 graphics card, the factory gives PSU as 550W, but I can't use 200W for full-speed CPU and GPU. In addition, the manufacturer's cooler cannot effectively dissipate heat at all, details refer my post:

https://www.dell.com/community/Precision-Fixed-Workstations/Precision-3650-change-case/m-p/8153964#M9890

I should be able to upgrade the psu?

I read your post - but due to my phones rubbish internet browser all the posts are messed up and I couldn’t figure out your solution. Would you mind telling me your solution so I will get an email with your reply where I would be able to read it. 

You can go to path "Precision Fixed Workstations" and see my post "Precision 3650 change case?" for reference.

In general, thermal throttling won't make the i9-11900K perform well unless you retrofit the water cooling radiator yourself or change the case.

you can also increase performance, once you get your CPU heat issues under control, with the Intel XTU utility too.

https://www.intel.com/content/www/us/en/download/17881/intel-extreme-tuning-utility-intel-xtu.html

Precision 3650 Spec Sheet.pdf

Precision 3650 Documentation 

I had tried to control from Intel XTU but that is not work due to all core-tuning be disabled/locked.

It can't even work on 11500.........  all core CPU running 3.7 only... when temp hit 80C around, CPU clock down from 4.2 to 3.7.........

I have upgraded VRM heatsink + 125W copper cooler already.