I think If the circuit of iontophoresis didn't change, the current was depending on the Input Volgate. 20V would give about 5-10mA according to skin resistance. Human skin resistance about 1K to 2K or more (it's variable). So if anyone want to increase the current, increast the voltage is necessary. (Of course, Must try to decrease skin resistance first). It's my opinion, I hope some suggestion or question about my opinion. It's not my exertise.