When using Picaxes, a 5VDC supply is required, and, when using other IC’s or equipment with the Picaxe, another DC supply (with common Gnd) may be also be needed (eg 3.3V,9.0V, 12.0V, 15.0V, 24.0V etc)
In a recent project I needed a 12VDC +ve supply as well as 5VDC +ve supply so went trolling...