Sorry for the tardy response. Power supply SIZE recommendations are listed in the build instructions:
Stepper Power Supply
The stepper power supply MUST be capable of providing 50% of the TOTAL current draw of the steppers. A 2.5A stepper will draw 5 Amps! For example: 4 steppers rated at 2.5A will draw a total of 20Amps. Adequate fusing must be used on both the AC and DC side.
Personally (and for testing), I use a basic, unregulated, linear power supply. A large toroidal transformer, bridge rectifier, filter caps and fuses. See the FAQ Power Supplies for the schematic.
Also, there are LOTS of cheap switch-mode 36V 10A supplies on eBay. I personally don’t like the use of switch mode supplies for huge inductive loads, but since I don’t hear/see lots of complaining about these supplies, so I can’t say “no”.