Can someone help me with this problem of mine?

[Forstride]

Last night, my mom brought a pair of retro, over-the-ear headphones home for me (She got them for free, so if I can't get this problem fixed, it doesn't matter). I noticed that they had a 1/4 inch (6.5 mm) jack. I immediately went to test them on my stereo system, and they worked fine. So today, I go down to my local RadioShack and pick up an adapter so I can use the headphones with my MP3 player and my laptop. I tested them a few minutes ago, and it only plays through the left (Or right, because there's no marking as to which side is which) side with the adapter. The headphones themselves are fine, but I'm wondering if I got the wrong kind of adapter...I got the stereo to stereo, but I'm not sure if I should have gotten the stereo to mono. Can anyone help me with this?

 

[outgum]

Im not a headphone professional or whatever, but you say it works fine in both without the adapter, and that its a streo to streo, maybe the heaphones are mono? So try a Mono to stereo maybe? Just an idea

 

[Forstride]

I'm pretty sure the headphones aren't mono, because it says "Stereo Headphones" right on the label on them. I'm going to get a mono adapter (I'm getting on both ways just in case) now, so I'll post my results.