Laptop charger tips explained: Dell, HP, Lenovo and more

Check the socket first

A charger works on a laptop when four things match: the shape and size of the plug, the voltage, the polarity and, on Dell and HP, the identification signal that tells the laptop what it has been plugged into. The brand on the lid is only a starting point. Dell alone has used three different connectors across its business range in the last ten years, and HP and Lenovo have each changed theirs at least once.

So when a customer puts a laptop on the counter and asks for a charger, turn it round and look at the socket before you look at anything else. A round hole with a thin pin in the middle, a round hole with no pin, a flat rectangle, or an oval USB-C port each send you to a different part of the shelf. The rest of this guide goes brand by brand, then ends with a short routine for checking before you order.

Dell: big round pin, small pin and USB-C

The big round pin is a 7.4mm barrel with a thin centre pin inside it. It was Dell's standard for years and is still everywhere in refurbished stock: older Latitude E-series machines, Precision mobile workstations and a long run of Inspiron and Vostro models. The small pin is the same idea shrunk to 4.5mm, still with a centre pin, and it took over on many Inspiron and Vostro models and the Latitude 3000 range from around 2014. Both run at 19.5V, so the only physical difference is the size of the plug.

That centre pin matters. It carries a signal from a chip in the adapter that tells the laptop the adapter's wattage. If the pin is bent or snapped, or the adapter cannot identify itself, a Dell will usually warn at start-up that the adapter type cannot be determined, then charge slowly, refuse to charge, or hold the processor at a low speed to save power. Customers often read this as a dead battery. More often than not it is a worn or damaged tip, and a new adapter of the right type fixes it.

Newer Latitude, Precision and XPS machines charge over USB-C, covered at the end of this guide.

HP: blue pin and big round pin

HP's blue pin is a 4.5mm plug with a centre pin and a blue collar on the tip, which makes it the easiest connector in the trade to recognise across a counter. It replaced the older 7.4mm big round pin on ProBook, EliteBook and HP consumer models from around 2013. The big round pin is still common on older EliteBook and ProBook stock, and both run at 19.5V.

Like Dell, HP uses the centre pin to identify the adapter. A Dell 7.4mm plug will physically go into an HP 7.4mm socket and the other way round, but the identification signal is not shared, so the laptop may refuse to charge, charge slowly or show a warning about an unrecognised adapter. Sell the brand that matches the laptop, even when another brand's plug fits.

Lenovo: the yellow rectangle and the round pins

Lenovo's slim tip is a flat rectangular plug, usually called the yellow rectangle in the trade. It arrived with the ThinkPad generation of around 2013 and spread across ThinkPad and IdeaPad models for the next several years. It runs at 20V, against 19.5V for Dell and HP.

Before the slim tip, ThinkPads used a large round plug of about 7.9mm with a centre pin, and many older IdeaPads used a plain 5.5mm round barrel with no centre pin. Both are sold as round pin adapters, so check which one a laptop takes before ordering, and ask us which tip a pack carries if the listing does not say. Most ThinkPads from around 2018 onwards charge over USB-C instead.

Toshiba, ASUS and Acer: round pins that look alike

These three brands mostly use plain round barrels at 19V, and that is where wrong sales happen, because the plugs look almost identical. Toshiba Satellite and Tecra models commonly take a 5.5mm outer, 2.5mm inner barrel. Older ASUS models use the same 5.5 by 2.5mm size, while many slimmer VivoBook and ZenBook models take a smaller 4.0 by 1.35mm plug. Acer's Aspire and TravelMate ranges most often take 5.5 by 1.7mm, and some thin Acer models use 3.0 by 1.1mm.

The trap is the inner diameter. A plug with a larger inner hole will slide onto a thinner pin but make poor contact, so the laptop charges on and off as the cable moves. A plug with a smaller hole will not go on at all. A cheap pair of digital callipers on the counter settles it in seconds: measure the outer diameter of the old plug, look into it for the pin size, and match both.

USB-C, and a routine before you order

USB-C is the same shape on every brand, but shape is not the whole story. The laptop and adapter agree a voltage through USB Power Delivery, and the adapter's wattage decides whether the laptop charges properly, slowly or not at all. That is a separate subject, and our wattage guide covers it.

Before ordering a pack of 100, run the same four checks every time. Read the output on the original adapter's label, or the input rating on the base of the laptop. Measure the plug, and note whether it has a centre pin. For laptops bought by the lot, read the charger column on the lot's spreadsheet, because most units ship without one. And if you are still unsure, send a photo of the socket and the laptop's model label to us on WhatsApp before you buy.

One last point: our charger packs are adapters only, with no mains cables in the box. Most laptop adapters take a clover-leaf lead, so order a pack of UK clover power cables alongside them.