What power supply required for my ECS Elite EZX15G. 12v 3A ok but is it + or - tip? Thanks Roger

Normally (90%) it is center positive. The larger outside is effectively 'Ground' and not only connects the inside socket securely to the motherboard, but also provides massive support to keep it aligned and attached by connecting to the most massive copper parts of the PC Mainboard inside. In most cases (pun intended) there is a diagram of a C with a o inside somewhere near to the connector on the PC which tells you which is definitely which. AC doesn't matter, so if its 12V 3 A ACV it makes no difference which is which... and in those same 90% of cases, there is a Diode on the Positive side which only allows POSITIVE (+) volts to flow in IF the other side is more NEGATIVE (-) so no worries... it will not smoke ;-)

Hope that helps