You can get a regular ATX power supply, it's more expensive but gets the job done and are readily available. You can also resell them to gamers when you're done if you have no further use for it. You can use more than one PSU just don't use two different PSU on one hashing board. If you want one ATX PSU with enough power and cables to power this and any other ASIC I recommend EVGA SuperNOVA 1600 P2 it's platinum efficiency and tons of power and PCIe connectors. They used to be easy to find refurbished for $230 on Ebay sold by Newegg but since the gpu mining craze I haven't seen any. The price for a new one is steep but if you plan to continue mining it's quit and more than enough power for an L3+ and whatever next gen ASIC comes out. Or if you ever get into GPU mining it could power a massive rig lol.
A cheaper option would be the EVGA 1300 G2 gold psu for the L3+, the 800-880 watts would be around peak efficiency for that so probably a better option if you do go the ATX PSU option. If you can find one used you can save a few bucks, the warranty on these is ten years I think, and I know EVGA warranty is transferable so if you buy used you're still covered. Just an extra thoght as a way to save since ATX is gonna be more expensive than the Bitmain PSU, they'll also be quieter though.