This one with free shipping and 17 quid less.
1/87 Ho Scale Train 50cm Track Model Accessories Train Treadmill Track Bearing Train Roller Test Stand With 8 Rollers Kids Gifts - AliExpress
Woking Pre Assembly Depot was mostly built on loco ash. Once a month or so the local fire brigade would turn up and spend a few hours hosing the ground down, as deep underneath it was still smouldering and that was back in the late 70's early 80's.
Also, along with the reply above, have you connected the handset to the right hand socket on the board with the red led? ( led to the top )
I did plug in to the wrong side once and found nothing happened, no control or programming.
It's not a wall-wart, it's a transformer with a lead and UK 3-pin plug ( which will have a fuse in it. ) Hornby HM700 R7337.
I would imagine the PSU has over current and short circuit protection built in.
Wondering if that blade wasn't far enough mid-way to stop the little metal tag underneath the blade from making a connection, that might have given the false reading on your tester but as you say the fault seems to have cleared itself.