[PSU]How much is too much?

I'm wondering how many devices can be plugged into the same power cord while still being considered safe. I was always told to never plug two hard drives on the same psu cord, but I'm wondering if this compares.

I've got one cord coming out of my psu --> 2fans --> hard drive --> DVDrom

wondering if thats too much for one cord. PSU is a Corsair CMPSU-620HX btw.

I'v had 4 harddrives plugged into the same cable, no issues.

The thing you need to take into consideration is that the powersupply breaks it's amperage output across multiple rails; usually 3 or 4. Two for the motherboard (one for the ATX24V and ATXP4, another for the 5VSB) and two for molex connectors although I'v seen supplies with 5 or 6 rails. One chain of molex connectors can be hooked upto the same rail as another; it all depends on how the supply is wired. Harddrives usually draw under 10 watts (2 amps at the most) while cd-rom drive usually draw under 5 at peak usage. My 500W powersupply will deliver upto 12 amps on the external rails. It all really depends on the total wattage output of a PSU. It tells you what the supply on the side can handle.

Generally, if you overdraw a power supply rail the system will start crashing, refuse to start up, or blow a breaker if you're unlucky. As a general rule of thumb, never use molex doublers (converts 1 molex connector into 2).