Can I imitate purple (5VSB) wire by using 5V (30W) adapter joining ground of PSU and ground of adapter and using +5V wire instead of the purple?
Both PSUs (new and old) are from same manufacturer but only difference in power and this purple wire. The 5V adapter is different small like a raspberry 3A USB adapter.
I know that something can be damaged if I do something wrong, but (Without damaging something)
So as long as you use less than the power that the supply can provide, and the 5V consistent enough, it should work.
See also https://electronics.stackexchange.com/questions/596489/where-can-i-get-5vsb-from-a-motherboard for potential alternatives if you are having difficulty finding a place to get 5V to feed your device (some boards can generate 5V from 12 for example to feed USB peripherals and the like).
