關機後無法按下電源開關開啟，必須要拔掉插頭才能開機

因為我目前遇到關機後無法按下電源開關開啟，必須要拔掉插頭才能開機，在網路上找到 這篇相關討論。

Metzen 說明為什麼當關機之後，無法按下電源開關開啟，必須要拔掉插頭，才能開機成功，原因在於 PSU 廠商為了節省成本，沒有投入資源設計可以正確偵測 5V OCP，而是使用降規的 12V 線路，導致過於敏感與緩慢的充電。

不知道是否有網友可以協助我跟深入了解背後的電子學原理呢？我目前使用的 ASRock J3455B-ITX 搭配 12V轉 DC-ATX 電源模組，與台達電的 DC 變壓器，就有這樣的情況。

The PSU detects 5V on power on within 100ms or so and if it's in a certain range (> 0.8V or so) then it would NOT turn on. Hooking this up to an oscilloscope verified the issue. On power-off the 5V line would NOT discharge within a reasonable amount of time (up to 10 minutes to get < 4.5V) and attempting to power the unit back on would trigger the OCP (over-current protection) circuit, causing the failure your experiencing.<br>
Exploring further, tried artificially loading the 5V line with resistors (20W worth) to expedite the discharge rate. It worked well enough to bring the discharge time down to ~15secs or so.

Exploring even further then that, we went back to the PSU manufacturer and found that the whole thing was caused by them not wanting to devote engineering resources to a proper 5V OCP detection circuit. They just recycled the 12V detection circuit and stepped it down making it both overly-sensitive and cause the slow discharge. 8 weeks and forcing the issue with their management we got our fix and it works perfectly.

You'd probably be *shocked* to find out that ASUS boards are actually a leading symptom of this. The PSU manufacturer would have rather taken the few losses of sales vs. actually fixing the issue when they calculated their risk assessment vs. $$ spent to fix it.