Quick polarity question re: 18V 1970's EHX pedal - Help appreciated

[tj7]

for my 18V 1970's electric mistress flanger, i have purchased a regulated DC power adaptor with multi-plug output adaptors and selectable polarity. Accepts input voltages from 90 to 260 Volts AC. DC output voltages are 5, 7.5, 12, 15, 18, and 23 V DC, with maximum current of up to 1000mA.
it includes the correct 3.5mm TS connector.

polarity question: the connectors can be hooked up in one of two ways, of course:
should the centre / tip of the connector be positive or negative..?
ie do i want the "+" lining up with "CEN" or not...?
thanks in advance...

[cpm]

usually, tip +, sleeve -
but you can always make sure, following the path from the jack to the circuit, where ground is usually indetifiable