Don't buy this style of Christmas light

Thankfully the sellers of strings like this are going in the direction of selling USB or battery based ones instead - not because they care about your safety, but purely because they are cheaper for them to buy and make more profit from. This style is still widely available though and has many safety issues. The wire is ultra thin and only single insulated meaning that it can easily be damaged and a short circuit poses a genuine fire risk. The LEDs have no wire strain relief and a very thin insulating sleeve that solder spikes can sometimes pierce exposing live connections. The controller has a flimsy clip on cover that can easily pop off (sometimes during shipping) to expose live electrical connections. The sellers on platforms like eBay often claim these lights are suitable for outdoor use. They are absolutely NOT suited to outdoor use. The open ended sleeves around the LEDs can wick water in and pose a shock risk, and the water will also corrode the LED leads and make sections of the lights fail very quickly. I recommend buying light strings from local high street retailers with accountability and a reputation to protect. They will generally sell LED strings with safe SELV (Separated Extra Low Voltage) plugs.