How you use UCC? Well, our smallest product, Model 1515, uses 2 UCC. Hence, 40mF is being used, and it is very small - 0.25mm x 15mm x 15mm
I'll furnish the details on Voltage and so on later.
So you presure 40mF (or 20mF) into such a small space. Without checking numbers if you have designed it for the usual max voltages of a few volts that must result in a high(er) energy density storage. That explains the high price.
Would really like to know the energy density you archive and how you do that. There are physical limits.
That sounds interesting to me from a technical point.