Dummy double C-type battery for 3 v appliances - Preliminary hypothesis

Appliances powered by 3V with two 1.5V type C batteries in series are always present on the market while the availability of these batteries is increasingly rare, with costs that are not exactly cheap.

I tried using a 3D printed adapter that allows you to simulate a C-type battery with a 1.5v AA-type battery (i.e. https://www.thingiverse.com/thing:39182), but this solution draws little current and the smaller cells have limited total energy capacity.

Since it's getting easier and easier to find old unused desktop ATX power supplies, with very little modification you can easily get high current levels at 3.3v (in addition to the other 12v and 5v outputs), so I'm trying to design an accessory to be mounted on the 3.3 v output (orange wires for the positive and black for the negative) to replace two type C batteries in series.

WARNING: this project is in a preliminary phase, it is published to evaluate its possible interest and to accept suggestions and criticisms.