Late but I found a power supply tester on amazon that looks pretty handyhttps://www.amazon.com/CRJ-24-Pin-Switch-Jumper-Sleeved/dp/B01MSY4966/ref=sr_1_17?keywords=power+supply+tester&qid=1576294227&sr=8-17
Although that's not expensive, the paper clip does the same for free.'I have one of these:https://www.amazon.com/Comidox-Computer-Supply-Tester-Automatic/dp/B07J9LRC6T/ref=sr_1_11?keywords=power+supply+tester&qid=1576335019&sr=8-11. It's a tad better than just a switch/clip, it also tells the voltages and Power Good time. Basically it's a dedicated multimeter. What's common with these cheap testers is that they don't tell how the PSU works loaded.
That's Dang near identical to mine...but I paid nearly $30 around 9 or 10 years ago....They do come in very handy