Cheap power supplies cause HDD failure.
I think this is aimed at mobile phone chargers, but the same applies to the AC power adapters for hard disk drives. A few years ago it used to be quite common to find external hard disk drives to be packaged with a European mains supply with an adapter to convert the plug to a 3-pin British socket. Fortunately as the price of hard disk drives has decreased the temptation for UK suppliers to import cheaper stock from continental Europe has declined, and nearly all new hard disk drives are now provided with a dedicated 3-pin British plug power supply.
Cheap replacement power adapters are not recommended. Desktop 3.5″ hard disk drives require a stable 12V supply, It does not take a significantly higher voltage to result in a failure of the printed circuit board of the hard disk drive, leading to a serious failure of the hard disk drive. The same goes for cheap power supply units (PSU) in desktop computers. A PSU can cost anything between £12 to £100. It is certainly worth spending at least £40 on a decent branded PSU; they are more reliable and more efficient.