Dual power supply ?

Dual power supply would solve that, but it's not really a problem. A few percent change in speed does not significantly affect extrusion properties.

The PID controller can handle 5 amps. The heater currently draws 3.3A. You should not increase heater power, for two reasons.

1.) it is not safe. in the event of user error or controller malfunction, the maximum temperature must be limited to below what would offgass toxic byproducts.
2.) you need to give the slug of plastic in the barrel time to melt. increasing heat would not help with this, as getting hotter faster will only serve to cook (carbonize) the outer layer while the core is still solid.

The source is DEFINITELY not too far from the nozzle. In fact insulating the barrel will increase output rate, as it preheats the pellets.

1-2A.