Hello danboid,   I don't have an exhaustive list, but I was able to verify this Customer Kit for NVMe drive , in the R7515, does have that carrier:   Part# 400-BKFR - Dell EMC PowerEdge Express Flash Ent NVMe Read Intensive U.2 Gen4 3.84TB with Carrier [URL] It not stated on that page, but drill down of the part shows it contains this carrier : DXD9H - ASSY Carrier HDD/SSD, 2.5 Inch, Metal     Are you able to verify your backplane is seated correctly? Maybe remove and reinstall - Page 51 - [URL]     Can you provide some pictures with it in the caddie and the alignment issue?  
We recently purchased a PowerEdge R7515 with a PERC H740P Mini RAID controller and a 24 bay chassis configured so that slots 12-23 can be used with U.2 NVME disks. In addition to this we purchased 10x DXD9H disk caddies, 6x Samsung SATA SSDs and 4x Samsung PM9A3 U.2 disks from another company. The DXD9H caddies work fine for inserting the Samsung SATA SSDs but they are not quite right for the PM9A3 U.2 disks. The PM9A3 disks fit into the caddies fine and you can insert the disks most of the way into the (U.2) bays but they don't connect to the interfaces when in the DXD9H caddies because the connectors are not aligned correctly by a few mm.  We have been able to attach, use and boot from all 4 U.2 disks when they are connected without housing them in caddies so the drives are electronically compatible and the disks work but they're not very secure having them inserted loose like that.Is there a special caddy for using U.2 disks in a R7515 or maybe there is some kind of adapter required to house disks like these?   [IMAGE]
Using Samsung PM9A3 U.2 disks with a PowerEdge R7515