The Sinclair ZX80 was the most popular personal computer in Britain at the beginning of the 1980s, due to its low price which was enabled by extreme minimalism; it consisted of not much more than a Z80 CPU and a kilobyte of static RAM, with an edge connector to which RAM expansion could be connected; according to https://en.wikipedia.org/wiki/ZX80#rampack
Other than the built-in cassette and video ports, the only provided means of expansion was a slot opening at the rear of the case, which exposed an expansion bus edge connector on the motherboard. The same slot bus was continued on the ZX81, and later the ZX Spectrum, which encouraged a small cottage industry of expansion devices, including memory packs, printers and even floppy drives. The original Sinclair ZX80 RAM Pack held either 1, 2 or 3 KB of static RAM and a later model held 16 KB of dynamic RAM (DRAM).
But as I understand it, the then current 16kbit RAM chips actually required three different voltages: -5, +5, +12. And I don't see those in the pinout of the expansion connector: http://projectspeccy.com/documents/Edge_Connector_Diagram_ZX80.pdf
So how did the machine supply the necessary voltages to use dynamic RAM?