Currently I'm using SToM USB card, I'm not sure this USB card is enough or not.
If I replace stock power cable(at PSU), the sound might be better?
The only thing I have found that require a special power cable is to eliminate RF if you are having a problem with that. I have one tube amp that was particularly sensitive to RF and it did fix the problem.
Get a power conditioner (instead of your plugged extension lead/surge protector). These things do make a difference to a range of equipment. It's easy to tell the difference in my cases and has been more pronounced than swapping a £100 headphone amp with a £500 one in some cases.
A power conditioner by clearer audio is a good start.
There are better things in this hobby to spend money on.