If it explodes ("fire or bang") it could destroy a lot more than your computer. That said if any power supply dies, frequently there is an initial power surge. Not even overload protection can always protect against this surge and other components get destroyed. I was an electronics engineer in a former life and it is surprising how often this happens even with the most sophisticated protection. The way a PSU works, very very basically, is that it takes mains voltage, 240 volts OR 110 volts and drops it to 12 volts and 5 volts to drive your computer. If that high voltage, or part of that high voltage, gets on to the low voltage side then the components that only want to see a low voltage will be destroyed.
As far as buying a PSU for your computer buy the one with the highest wattage rating you can afford your computer will only take what it needs. Also go for well known makes. But don't think that even expensive branded PSUs are indestructable, they are not. Your best, by far, protection is to ensure that all your IMPORTANT files are backed up somewhere else other than your computer.