In USB terms, "more power" is technically anything over 2.5mA, realistically over 100mA. The original intention of USB was for host to actively limit the curre

In USB terms, "more power" is technically anything over 2.5mA, realistically over 100mA. The original intention of USB was for host to actively limit the current available. But before it started to be reasonably cheap to do so, everyone went with the simpler implementation of connecting VBUS to whatever +5V rail the device has (in more sane implementations thru some kind of (poly)fuse), with some standards that include USB even making it technically impossible to limit current by software (AGP, various late 90's "single cable to display" interfaces and so on) by not including any wires to do so. Even bus powered hubs typically just connect the VBUS together and when some downstream device does not obey the current limit, the whole thing just fails randomly.