If they're identical power supplies (exactly the same voltage, current, impedance, phase) then yes. At a minimum they must have the same output voltage and be connected in proper phase. But if there are significant differences, they may "fight" each other, sending power back and forth to each other which limits power available to an external load. Even without power exchange there may be unequal load sharing, so one supply carries more than half the load and the other less than half. So it's risky. If you do make such a connection, beware of heating and unusual sounds indicating excessive current. If you can, measure the input power and make sure it's reasonable compared to the output power.
If by AC power supplies you mean inverters run from a DC source, then all bets are off. These generate AC frequencies determined by an internal reference. Even if the references are accurate, they must be synced to stay in phase. If there is no means to sync them, don't even try connecting them in parallel.