Traditional Chinese Medicine (TCM) generally use inductive spikes so the spikes are current sources and the needles provide low resistance of some value ( Not checked <10k Ohm?) So the voltage and current are very short in duration, which can be computed and the Power = Voltage * Current and times time = Energy which may be more of a factor. Then the muscles respond to stimulated pulses at a higher threshold which in turn stimulates the body's reaction to heal itself with a skilled practitioner.
So the specs would be for mA current max and possibly the inductance behind that current where a voltage can be generated much higher than the charge voltage according to the resistance in the path V=IR.
Generally I think 1 mA pulse into acupuncture needles might be 10K so V=1mA*10K = 10 V which would feel like a 9V battery on the tip of your tongue for a short pulse.
These can be measured in Joules ( or milli-joules [mJ] ) where 1 mJ = 1mW * 1 second or 1W for 1 millsecond or the current stored in the small inductor as E=1/2L*I^2 then released as a spike then they can vary the current or charge voltage and charge duration is fixed. But in your case I don't know. It may be the equivalent of 100V into 10K ohms for 1ms but electrode R rises from chemical reaction until turned, unless using patches.
The time constant of the discharge depends on contact resistance between two wires such that the internal inductor L and skin electrode pair, R becomes T=L/R = time, and the voltage, V = I * R or peak current * electrode pair Resistance , R.
For example a 9V battery across the tongue if a long duration compared to 1ms but comparable to the energy felt in acupuncture adjustments if the patient can handle it. More is better but, it is supposed to be comfortable not torture. But if you have migraines, then you know what torture is.
With more time, I could have a better Engineering spec, but this is off-the-cuff.