Case History: A Quick Summary
As a matter of fact, computer cases have not changed very much over the years. In the middle of the 90's the CE-standard was introduced in Europe, forcing manufacturers to stick to these regulations. Cases had to be shielded, both acoustically and electromagnetically. In order to conform to these standards, a larger quantity of metal was processed, because all sides of the case had to be covered with appropriate metal plates. A front cover consisting of a plastic panel was no longer sufficient.
Thereafter, the ATX standard found its way to the mass market and gradually replaced the AT standard. The main change involved the motherboard layout, as it was now installed vertically instead of horizontally, leaving the processor in the air flow of the power supply fan. The connectors for keyboard, mouse, serial and parallel ports were placed directly onto the motherboard and were made available from the outside by an special cover at the back of the case.
In addition, the two confusing power connectors were replaced by one that is safer. By the way, the introduction of the ATX form factor made it possible to start and to shut down the computer via software for the first time.
The Power Supply - Plant And Regulator
With the transition from AT to ATX, a new power supply became necessary. Though there have been no significant changes to case design since then, an ATX power supply from 1996 won't be able to run a modern system - even if the power output might seem to indicate otherwise.
Modern cases are usually shipped with a power supply of 300 Watts. However, the power output is secondary in most cases, since it mainly determines the amout of consumer load. Today's computers require high currents of +5 V, as this is the supply to the processor and the graphics card. A rough role of thumb is that you need at least 25 A at +5 V, or, the more the better. There's certainly not much of a chance that future systems will require less power...
Therefore upgrading older computer is sometimes a pain, as the power supply is usually unable to cope with the requirements of an Athlon or the Pentium 4.
The best solution is to get a high quality power supply, e.g. from Seasonic or Enermax. These products not only offer excellent specs, but are characterized by quiet fans and USV-like qualities. Missing phases or phase variances can be bridged, which effectively protects against fluctuations within the electricity network.