There are quite a few different types of plugs that you'll find at the end of different light sets. Some are just manufacturer preferences, some are specific for types of lights, and some are designed to meet electrical standards of the sets themselves.
For most mini lights you'll find fused male plugs, fused plugs have a small electrical fuse inside the plug (usually protected by a sliding door) so that if there is an overload in the wire or problem the fuse takes the hit, not the bulbs. Fused plugs are also found on low bulb count C7 and C9 stringers sometimes. You can usually spot if a plug is fused because the plug itself is rather large and will have some sort of door for opening the fuse compartment.
For small bulb count mini lights you can sometimes find stack plugs. Usually mini light strings with 35 or less bulbs come with this style of plug so you can stack the plugs for craft projects. The male plug has a female connection on the back so you can stack the plug with other plugs.
Some style of Christmas lights have detachable or specialized plug that allow you screw multiple sets together. Some rice lights (ultra rice sets) have this type of separate power plug and all the Commercial quality LED sets have specialized removable power plugs.
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Zach
