Originally at the time of ATX 2.0, a power supply featuring "multiple +12 V rails" implied one able to deliver more than 20 A of +12 V power, and was seen as a good thing. However, people found the need to balance loads across many +12 V rails inconvenient, especially as higher-end PSUs began to deliver far greater currents up to around 2000 W, or more than 150 A at 12 V (compared to the 240 or 500 W of earlier times). When the assignment of connectors to rails is done at manufacturing time it is not always possible to move a given load to a different rail or manage the allocation of current across devices.