Oddball issue with DVD playback on PS2

[ZackN920]

Honestly I have no clue where to go with this thread. Seems like the video game section is almost dead, and this doesn't really fit in the best there either...

Anyway's I've got an "old" (fat) PS2 that I've had since new in the early 2000's. This thing has gotten heavy use as I was growing up. Parents would say way too many hours wasted on it.lol I've kept it up though(clean the vents periodically &ect.) It still plays everything as it should but I've noticed a weird issue with DVD playback lately(which is what I use it more for now).
While playing a show the picture will get dark, then after about 30 seconds or so, it'll brighten up to normal for about 5 seconds then go dim again. It just repeats this all the time, from the minute the DVD is loaded. All the menu screens on DVDs do the same exact thing. I know for a fact that this is not an issue with the VCR the signal goes through or the TV. That and video game playback doesnt have this issue.
I'm thinking there might be an issue in the power supply... But that's just a hunch. I honestly have no clue with this thing. What do you all think?