The 'safety switch' being the earth leakage breaker, the circuit breaker, or a combined unit (both)?

Hmmmm... if it's the CB that tripped, it sounds like the OEM PSU failed into a closed circuit and thus tripped the CB. You'd better hope the DVR didn't get any sort of voltage spike as a result and fry. If you're really unlucky, it is also possible that the DVR itself could have failed and thus fried the PSU thus tripping the CB. Just something to keep in mind Click here to enlarge

If it's the ELB that tripped, you might want to consider taking a good look over your current DVR setup and make sure everything is as it should be. There has to be a leak to earth to trip the ELB, and 19V isn't going to leak to earth any time soon - 240V sure will though!

In any case, does this DVR run 24x7? If so, it would be a good idea to get a PSU that can handle the 2.21A with real ease. The 3.4A replacement you mentioned should be adequate, assuming it is genuinely capable of a continuous 3.4A. Check to see if it gets uber hot during use.