The original IBM PC supplied several voltages: +5 V, −5 V, +12 V, and −12 V. Which computer supplied the most DC voltages?
To facilitate the comparison, let's agree on some uniform criteria for what counts:
- Only DC supply voltages count. AC line voltages (typically 120 or 240 V) do not count (they are not DC). Analog signals do not count (they are not a supply voltage).
- Do not count ground / zero volts. Thus, a "single-supply" computer counts as one supply voltage.
- Negative voltages count separately from positive voltages. Thus, −5 V counts separately from +5 V.
- Two or more supplies with the same nominal voltage only count once, even if they come from different circuits. So a regulated +12 V and and unregulated +12 V count only once.
- Voltages created on-chip (e.g. by a charge pump) count, if you can specify their amount.
By these rules, the original IBM PC had four supply voltages.
I suspect that a vacuum-tube computer might be the winner.