Alright, so I was going to install Source Film Maker but I didn't have any space, so I decided to connect an HDD via an USB converter(image below). I shut down the machine, turned the PSU off, and connected via a Molex connector & the USB converter. I turned back on the PSU, no sparks or anything, everything normal, but when I turned on the machine, I heard some sizzing(lol?) and sparks flying and a little flame, but the PC was running fine.

I pressed the power button instead pulling out the plug (I panicked) so it continued to short circuit for about 10 seconds. There's a very little part on the HDD that become ash, it's near the Molex connector and the circuit is a little black as well. I'm afraid that I will damage the HDD more so I didn't hook up the HDD after all. Do you think it's the PSU(came default with Cooler Master Elite 430, 500W) or it's the HDD(Samsung SP1203N)?

P.S: I've attached the HDD same way before(like 3 months ago), and it worked.

HDD burn:

USB connector:

Sorry for the bad image quality, taken with my phone.