Hard drive caddy 3.5” to 2.5” bracket adapter?

fyi, there are some official Dell 2.5 adapters which fit into the existing 3.5 caddy listed on ebay. Cheapest ones are from China.  However, you will almost certainly discover the existing right angled SATA power cables will not reach the newly installed 2.5" drive, particularly if you have a second 3.5" regular hard drive fitted.  ie. you will require additional SATA data and power extension cables.

As you have an MT case, there is space above the existing hard drive cage to mount a SSD by bolting one side/edge of the SSD to the perforated front metal panel. You will need some screws and washers.  The rear facing side of the perforated front panel is not completely flat in some places, so take care when tightening the screws - I recommend using some washers between the SSD and the front panel to prevent distorting the SSD case. New SATA power extension cable and possibly a new data cable will be required.  Note there was enough space for me to use cables with straight plugs..

Amazon used to sell 2.5 to 3.5 hard drive metal brackets which came as a pair.  I use one of these brackets between the SSD and the perforated front panel.  It should be possible to align the holes in the bracket with certain holes in the perforated front panel.  Unfortunately, I can't seem to find a listing for such pairs of brackets on Amazon, but a low profile 2.5 to 3.5" mounting tray may be a possible substitute provided it is not too big.

Here is a crude DIY solution using offcut of 7mm laminate flooring and cable ties.  Uses existing 'right angle' SATA data and power cables from previous hard drive.

Ooops!  I cut the boards half inch too short. So I had to add the red plastic extension piece.

SSD in top, hard drive in bottom bay. The SATA power connectors are deliberately offset to avoid severely bending the wires between the two connectors.