Small form factor Dell GX620 systems were plagued by bad capacitors. Some in the power supply, others on the system motherboard. I don’t recommend replacing components in the power supply, but the capacitors on the motherboard aren’t too hard to replace.
If your Optiplex 620 power light goes amber, or the system starts shutting down due to “thermal events”, open the case and check the five capacitors I have highlighted below.

five that should be replaced
If the top of any of them is bulging at all, (or leaking like the one in the back of my picture) you should replace all of the ones I’ve highlighted. You can order them from an online source like CapKing for less than $4.
I am not a pro at (de)soldering by any means, but I was able to remove the board, replace the capacitors, and re-assemble the system in about an hour. I’ve replaced them on two systems so far and both systems are running like new.
Here are links to the parts I used. (UPDATED: 8/6/2010)
1800uF 8mm 6.3v (x1)
2200uF 10mm (I’ve talked to the website owner and these are out of stock)
2200uF 10mm 10v – these should be used instead (x4)
Good luck, let me know if you’ve tried this and how it turned out.
Thank you for putting your message online. It sure has helped me and probably
many others.
I have replaced the 5 on 4 computers and they are running fine. Thank you for the info.
Another thought: Typical caps have a 20% tolerance. 20% of 1800 uF is 360 uF. Should be fine with any value reasonable close to 1800 uF thus.
Hmm, can’t find a 1800 uF cap here, but both 1500 uF and 2200 uF are easy to get… Anyone tried using either of them instead of the 1800 uF one?
Guess I could parallel a 1500 uf with a 330 uF to get a 1830 uF… Should be close enough.
power-on problems are one of the most common symptoms of these bad caps, since they are involved in the power regulation
Hi!
I have a Dell Optiplex GX620 that starts rebooting a few times when I start the computer in the morning, but wait and let the computer restarts 2 or more times, and it starts running OK!!!. First, try to change the video card, but the problem continues, any ideas?
Greetings.
PD: I’ll look inside to find these capacitors to check them out!