The Jupiter Ace's Power Pack.

These are even more scarce than the ACE! The ACE power pack will get hot when in use, out putting 9V at 800ma via a 3.5 Jack plug.

The Jupiter Ace power supply is typical of early 1980s technology, consisting of a transformer, diode bridge and a smoothing capacitor. There is a thermal cutoff in series with the mains supply.

The DC output is unregulated, i.e. the voltage is dependent on the load. Nominally 9V, the output is actually 15V when not connected to the computer and around 10.8V when it is. Within the computer a voltage regulator drops this to 5V, but because of the large voltage drop needed to achieve this, the voltage regulator gets rather hot. The computer draws around 640mA. The power supply is rated at 800mA.

The thermal cutoff is a safety device. It is not known whether it acts as a switch and will reset if it trips, or whether it acts like a fuse and would need replacing. Note that the smoothing capacitor is only rated at 16V which leaves little voltage margin when the computer isn’t plugged in, so it’s better to plug the computer in before switching on the power supply at the mains.