Safety when using ATX power supply as benchtop supply
It's quite far from certain death (indeed, it's voltages "generally recognized as unlikely to be hazardous", but we just had a big long discussion of that starting from a more hazardous and less useful premise.) Summary - you're a lousy conductor, you won't carry several amps at those voltages. Doesn't mean you can't make a big messy spark, or start a fire, but it won't electrocute you if you leave the box closed, unless you walk off into very marginally possible or probable scenarios.

The simple answer if you want a small-amperage supply is some in-line fuse holders with fast-blow fuses of whatever size floats your boat. If a quarter-amp suits your needs, it does not matter if the supply can provide 50 amps. You won't pull much more than 1/2 amp for a very short period before the 1/4 amp fuse vaporizes.

The short-term probably more expensive, possibly long-term cheaper option is DC circuit breakers.