Help with my step down converter please?

here's the situation im in, ive just purchased a Randall Warhead from ebay, love it. but in order to use the amp I had to buy a step down converter (I live in the UK and the amp is from the USA) well everything seemed fine but last night I tried to turn on the step down converter, and basically it kinda turned on and then went dead, nothing. the next day, out of pure hope I tried turning it on, and it came on! and it seemed ok. then a few minutes ago it did the exact same thing. I dont get it, does anyone with more electrical knowledge know why this could be happening?

Sounds like a dodgy converter to me...

Is it properly sized? Usually when something comes back on after its been off a while its a thermal/protection issue in one of the devices.