If you CPU is Intel Core X, you will need to get UDIMM such of this.

Assuming your system is the 5820 (I don't think there is a 5280 Precision) and following up on what @Chino de Oro has correctly posted, this is from the service manual specs for your system:

Specifications

Type

● DDR4 ECC RDIMMs - Supported with Xeon W Series CPUs
● DDR4 Non-ECC UDIMMs supported with Core X Series CPUs

Hello Collegues.
Got an used Precision5280T,  i7-7820x - with 2x16GB TP9W1 RAM Modules. Runs fine.

As this system has 2 Mem Controllers, I assume, having 4 same Modules allow better memory bandwith. Correct?

I couldn‘t find these specific RAM Modules anymore. So I bought a 4x16 Set

DDR4-RAM Vengeance LPX Black 2666 MHz 4x 16 GB CL16-18-18-35

replaced the 2x16 GB originals, tried to start with only the 4 Corsair banks.. but beside some sad booops, the system did nothing, and went off 

Afterwards I re-installed the original RAM, System startet perfectly.
A 2nd check, with only 2 of the Corsair banks: boops and off.

Do I have to replace with e.g 3200 16cas Modules 4x16 instead?

Corsair Vengeance LPX. 4 x 16GB, 3200 MHz, DDR4-RAM, DIMM

Thanks for advise.

michael