well that’s another issue - but it may be less of a headache to get the barrel swapped out if teh electrician agrees - it’s either that or the receiver on teh OT but any tech guy will know in a few seconds where the issue is - especially if they can offer up a 6v 3a power cable with the right barrel type/polarity to test - it’s an easy thing to detect and fix - but taking it to a person charging by teh hour may be more costly than sourcing a new psu if they’re setting minimum charges - all depends i guess, but teh part is cheap and the low skill job can be diagnosed and done in a few minutes tbh
needs to be a decent barrel like the one shown, good for a few amps - some thin metal cheap ones are rated for low amps <1
and wired centre positive obviously as per specs linked - 10 mins tops all in