Extra power from attached HDD Is it bad?

[DecoyObvious]

Hi all,

Just getting into this whole Mister thing, so please forgive my ignorance.

I plugged in an external HDD that uses a Y-split USB cable for extra power. The extra USB plug is connected to a separate power source, not a 2nd USB port on the Mister hub.

Anyway, when I flip the power switch off, everything seems to stay powered on until I also disconnect that USB power for the HDD. It would seem that the Y-split cable will send it's extra power seemingly to the HDD, and also back up the line to the Mister itself through the USB hub. So my question is, is this harmful? It feels like it might be sketchy to have power coming in to the system from both the regular wall adapter and one of the USB ports at the same time, but for all I know these things are designed to manage that.

I'm using the USB hub that comes with the pre-configured Mister set from Mister Addons.

Thanks so much for any help.

[darksakul]

Your MiSTer and HDD should be fine

[DecoyObvious]

That's a relief to know. Thanks for the response. Cheers!

[N.Master]

I agree.
For testing it will probably not harm to have 2 power supplies, but it should not be a long term solution for some reasons :
1 - if one PSU have more voltage than the other it may disturb the feedback of the switching power supply. A diode after each PSU can prevent that behaviour but quite often there is not always such protection "out of the box"
2 - if one PSU fails the remaining PSU can be overloaded .
3 - if you forget to plug both PSUs at the same time you will have problem n°1 + problem n°2
4- you will create ground loops and supply loops, and that can cause a lot of erratic problems.