This is what Leadshine say

"Regulated or Unregulated Power Supply
Both regulated and unregulated power supplies can be used to supply the drive. However,
unregulated power supplies are preferred due to their ability to withstand current surge. If regulated
power supplies (such as most switching supplies.) are indeed used, it is important to have large
current output rating to avoid problems like current clamp, for example using 4A supply for 3A
motor-drive operation. On the other hand, if unregulated supply is used, one may use a power supply
of lower current rating than that of motor (typically 50%～70% of motor current). The reason is that
the drive draws current from the power supply capacitor of the unregulated supply only during the
ON duration of the PWM cycle, but not during the OFF duration. Therefore, the average current
withdrawn from power supply is considerably less than motor current. For example, two 3A motors
can be well supplied by one power supply of 4A rating. "