This is a ZX Specrum Clone base on Harlequin by Chris Smith (http://www.zxdesign.info/harlequin.shtml). PCB is the same size as original ZX Spectrum, can be fit in 48K or 48K+ case.
Use standard ZX Spectrum Adapter, 9V with center pin negative (-) If you want to get PCB, you can get it from PCBWay through this link: