“There is no such thing as “stored voltage.””
Not sure what you mean. Voltage is the difference in potential that can cause current flow. Batteries and Capacitors store it. Also called a “Charge”.
I would say that this device would have to be a simple switching power supply storing a charge to a capacitor and then releasing it back through the 5V source.
That’s exactly my point. The “volt” is a unit of EMF, not “charge.”
Using the “volt” as a unit of charge is like saying, “How much water is in this jug? Five pounds per square inch.”