Review on 4-pack Low Voltage Inline Switch for DC 12V Power, Male to Female 5.5mm x 2.1mm Barrel Extension Cable, Ideal for LED Strip 5050 3528 2835, Light and Other Low Voltage Applications by Danny Kimble

I bought this to power my cable modem. Despite the correct outer diameter, it did not fit. It turns out there are two different sizes of 5.5mm hollow DC jacks. Both have the same outer diameter, but one type has a pin inner diameter of 2.1mm and the other is 2.5mm. This product is only compatible with pin sizes of 2.1mm. I thought they were one size, but I was wrong and wasted $8. Before ordering, be very careful and check the inner pin of the jack you intend to use it with. If it looks like a larger size, don't order it. It's a very small difference, but it bit me. I cannot rate this product as it was not inaccurate in its description but I still have a useless product. Revain requires me to give a rating to post this so I'm giving it 3 stars because the description should be clearer that there are different sizes of the 5.5mm jack and it's not universal.