Even though it is not hot, duct tape will still leave sticky residues.

For example, plaster to wrap your wounds. After you apply and leave it for few hours, or days, when you peel it off, you will feel sticky on that part right?

you need to remove it before sending for RMA, else its automatically rejected 

Alternatively should have bought psu with sleeved ready. The best bang for buck is gigabyte superb 550w which is around rm 170 with fully sleeved cabling. I've tried sleeved my acbel psu using vantec sleeve kit. Is a very messy task and you need proper tool to remove the molex pin. Worst is removing those 20 or 24 atx power pin. Use cable tie is the cheapest alternative which the least mess because duct tape will stick dust and dirty and times goes by.