What kind of power supplies?
If fairly close in characteristics, a small resistance in series could be added to help balance the current draw. If a resistance value R is placed in series with each power supply, For output voltages V1 and V2 at any given time and current draw i, the difference in current, i2 - i1, will be (V2-V1)/R and i = i2 + i1. You would want to choose the resistors such that maximum current draw allowed for either supply isn't exceeded at full load.
Any d.c. power supply can be described as a battery in series with a resistance. The resistance represents the drop in voltage as current is increased. Switching power supplies tend to have low series resistance compared to linear supplies.
The disadvantage of adding resistance is that it decrease the available voltage at full load and decreases the efficiency of the power supply. The feedback loop could be modified to place the resistors within the loop which will give better regulation but that can be tricky.