Power supply cable: what should you look out for when choosing a DC and AC cable?

DC cable — an underrated component that determines the quality of the power supply

Conductor cross-section: a thick cable does not necessarily mean a good cable

The most important parameter of a DC cable is the cross-sectional area of the copper conductors inside it. The thinner the conductors, the greater the electrical resistance — and this presents two problems:

Voltage drop under load. The current flowing through the thin wires causes the voltage at the end of the cable to be lower than at the power supply output. With devices that are sensitive to power quality (routers, IP cameras, readers, controllers), even a slight drop can cause unstable operation, resets or errors.

Cable heating. Thinner conductors also result in greater energy losses converted into heat. A cable that becomes warm under load is a sign that the conductors are too thin.

An important rule: The lower the power supply’s output voltage and the higher the current, the thicker the wires should be. At 5 V and 3 A, the wire cross-section has a much greater impact on the quality of the power supply than at 24 V and 0.5 A.

Beware of cheap cables: thick outer insulation does not necessarily mean thick conductors. In budget products, a thick rubber sheath often conceals conductors with a minimal cross-sectional area. The only reliable way to verify this is to check the technical specifications or measure the voltage drop under load using a multimeter.

Flexibility: a cable that doesn’t cause installation problems

A good DC cable should lie flat — in cable trays, behind furniture, and in bundles. A stiff cable is a practical problem: it is difficult to route, pushes the plugs away, and at low temperatures (e.g. in unheated rooms or outdoors) cheap plastics lose all their flexibility and become prone to cracking.

Cables with silicone insulation or high-quality PVC insulation containing a plasticiser remain flexible even at temperatures a few degrees below zero.

Mechanical durability: the cable must withstand everyday use

A DC cable by a desk is regularly subjected to: the castors of an office chair rolling over it, bending at the plug, and being tugged when reconnecting. Therefore, a good-quality cable should have:

• Abrasion-resistant insulation — will not wear through on contact with the edge of a desk or a cable duct,
• The bend guard at the jack plug and the casing — a flexible bend guard that protects the cable where it is subjected to the greatest mechanical stress.

The absence of kinks is one of the simplest indicators of quality — and one of the most commonly overlooked when assessing a cable.

AC cable — safety and ease of use are what matter here

An AC power cable connects the power supply unit to a mains socket. Although it may look unassuming, it must meet strict safety standards — and has a direct impact on the ease of installation.

Two or three cables — depending on the power supply

Double-insulated power supplies (protection class II) are connected using a two-core cable — they do not require earthing. Standard power supplies (class I) require a three-core cable with a protective earth (PE) conductor.

Using the wrong cable — for example, a two-core cable where a three-core cable is required — is a safety hazard, not just a technical one.

Plug: suitable for the country and the power supply unit

There are more than a dozen different mains plug standards in use around the world. An AC cable must have a plug that complies with:

• the standard in the country of use (e.g. type E/F in Poland, type G in the UK, type A/B in the USA),
• the socket on the power supply unit (IEC C13, C7, C5 and others).

Before buying a replacement cable, always check both ends — the national standard and the type of socket on the power supply unit itself.

Flexibility: a problem that silicone solves

Safety standards impose minimum requirements regarding insulation thickness and conductor cross-sectional area — and this means that AC cables, particularly three-core cables, are by their very nature thicker and stiffer than DC cables.

The solution lies in the insulating material. Manufacturers who use silicone compounds or high-quality PVC with added plasticisers produce cables that are flexible and easy to install — even though they meet the same standards as their rigid counterparts.

Practical tip: If the AC cable is going to be plugged in and unplugged regularly or routed through tight spaces, it’s worth paying for the silicone-insulated version. The difference in day-to-day convenience is noticeable — especially in winter.

Frequently Asked Questions

Why is the device behaving erratically, even though the power supply has the correct specifications? One possible cause could be a DC cable that is too thin — this causes a voltage drop under load. Use a multimeter to check the voltage directly at the device’s plug (not at the power supply’s output). A difference of more than 0.3–0.5 V indicates a problem with the cable.

Can I use an AC cable from another device? Yes, provided the plugs fit and the number of wires is compatible with the power supply’s protection class. Do not use a two-wire cable where the power supply requires an earth connection (Class I).

How do I know if a DC cable has the correct conductor cross-section? It is best to check the manufacturer’s technical specifications. In practice, you can also measure the voltage drop under load — if the difference between the power supply’s output and the plug exceeds a few tenths of a volt, the conductors are too thin.

What type of plug does the AC cable for a power supply unit used in Poland have? In Poland, the standard is type E or E/F (Schuko). The other end of the cable depends on the socket on the power supply unit — most commonly IEC C13 (as found on desktop computers) or IEC C7 (a small figure-8 socket).