You are referring to your example as current, but in fact this is voltage. In any case, for your example (ie. 100->400) you can use an amplifier to raise the voltage of this signal (or just add a 300mV voltage source if the signal is not changing). There are many low-noise opamps available. Every component induces some noise component, whether it be 1/f noise, johnson noise, etc.
If you want to pump your Volt then you can lower your AMPS so you have the same power so you can do it with the same power you don`t need a new Vcc and Vee
9V 100mA = 0.9W , 3V 500mA = 1.5W. You cannot suck from output more power as input. So for this output power (W) You need with 9V input - in ideal case - 170mA. With switching power supply (efficiency about 75...90%) also must increase the input current depending from efficiency....