我本人也遇到了这个问题，不知怎么触发的突然UPS断开连接，设置里识别不到UPS，重启UPS，重启飞牛，都不好使。
经过排查，结合AI辅助，发现是因为 /etc/nut/ups.conf 中的UPS序列号错乱，内容是乱码，长度不对，双引号不匹配。
通过手动修改序列号，并重启nut服务，成功识别UPS。具体操作步骤如下。
0. ssh登录系统，切换root用户,（执行后提示输入密码，仍然输入本人的密码，不需要知道root的密码）
sudo -i
1. 查看 /etc/nut/ups.conf，定位问题，执行
cat /etc/nut/ups.conf
回显 （省略大段注释文本）
[1413031]
driver = "usbhid-ups"
port = "/dev/bus/usb/001/006"
vendorid = "051D"
vendor = "American Power Conversion"
productid = "0002"
product = "Back-UPS BK650M2-CH FW:294803G -292804G"
serial = """0102000?""
bus = "001"
desc = ""
override.x.additional.lowbatt = "15"
override.x.additional.devicetype = "USB"
可以看到serial字段明显出问题了，我们手动连接UPS看看是不是这个问题，执行
upsc -l 查看当前UPS的 ID （或者叫什么码？反正就是一个唯一标识）
回显
Init SSL without certificate database
1413031
继续执行尝试手动连接UPS /lib/nut/usbhid-ups -a 1413031 -DDD (这里的 1413031 换成你自己的)
回显
USB communication driver (libusb 1.0) 0.43
addchar: discarding invalid character (0x0a)!
0.000000 [D1] debug level is '3'
0.001836 [D2] Initializing an USB-connected UPS with library libusb-1.0.26 (API: 0x1000109) (NUT subdriver name='USB communicatio
0.001845 [D1] upsdrv_initups (non-SHUT)...
0.004700 [D2] Checking device 1 of 5 (1D6B/0003)
0.004723 [D1] Failed to open device (1D6B/0003), skipping: Access denied (insufficient permissions)
0.004727 [D2] Checking device 2 of 5 (8087/0AA7)
0.004736 [D1] Failed to open device (8087/0AA7), skipping: Access denied (insufficient permissions)
0.004740 [D2] Checking device 3 of 5 (3151/6000)
0.004749 [D1] Failed to open device (3151/6000), skipping: Access denied (insufficient permissions)
0.004753 [D2] Checking device 4 of 5 (051D/0002)
0.006645 [D2] - VendorID: 051d
0.006653 [D2] - ProductID: 0002
0.006656 [D2] - Manufacturer: American Power Conversion
0.006659 [D2] - Product: Back-UPS BK650M2-CH FW:294803G -292804G
0.006663 [D2] - Serial Number: 9B2133A18027
0.006666 [D2] - Bus: 001
0.006669 [D2] - Device: unknown
0.006672 [D2] - Device release number: 0106
0.006675 [D2] Trying to match device
0.006679 [D2] match_function_subdriver (non-SHUT mode): matching a device...
0.006684 [D3] match_function_regex: matching a device...
0.006792 [D2] match_function_regex: failed match of Serial: 9B2133A18027
0.006796 [D2] Device does not match - skipping
0.006805 [D2] Checking device 5 of 5 (1D6B/0002)
0.006818 [D1] Failed to open device (1D6B/0002), skipping: Access denied (insufficient permissions)
0.006822 [D2] libusb1: No appropriate HID device found
0.006826 libusb1: Could not open any HID devices: insufficient permissions on everything
0.006829 No matching HID UPS found
可以看到明显的报错信息 failed match of Serial: 9B2133A18027，说明就是这个导致的，虽然不知道是什么原因，先手动给他改回去看看。
从上面报错信息显然可以得出，我这个UPS的真实的USB序列号是9B2133A18027，当然你的应该是和我不一样的，这个要改成你自己的
2. 确定当前处于英文输入法，执行命令打开编辑器
vi /etc/nut/ups.conf
用上下左右键定位到你要修改的位置，然后按 i 进入编辑模式，进行修改，修改后的文件如下，只需要修改序列号字段，匹配你自己的真实序列号，其他地方是自动识别到的，不需要和我展示的一模一样
（省略大段注释文本）
maxretry = 3
[1413031]
driver = "usbhid-ups"
port = "auto"
vendorid = "051D"
vendor = "American Power Conversion"
productid = "0002"
product = "Back-UPS BK650M2-CH FW:294803G -292804G"
serial = "9B2133A18027"
bus = "001"
desc = ""
override.x.additional.lowbatt = "15"
override.x.additional.devicetype = "USB"
3. 修改完成后，确定当前处于英文输入法，按 ESC 键退出编辑模式，依次按下 : w q 回车 四个按键完成保存，可以再次执行 cat /etc/nut/ups.conf 查看是否修改正确
4. 最后重启nut服务，执行
systemctl restart nut-server
5. 查看服务状态确定是否成功识别，执行：
systemctl status nut-server
回显：
● nut-server.service - Network UPS Tools - power devices information server
Loaded: loaded (/lib/systemd/system/nut-server.service; enabled; preset: enabled)
Active: active (running) since Sun 2025-10-19 02:24:44 CST; 17s ago
Main PID: 21031 (upsd)
Tasks: 1 (limit: 18664)
Memory: 624.0K
CPU: 4ms
CGroup: /system.slice/nut-server.service
**─21031 /lib/nut/upsd -F
Oct 19 02:24:44 N52 nut-server[21031]: fopen /run/nut/upsd.pid: No such file or directory
Oct 19 02:24:44 N52 nut-server[21031]: Could not find PID file '/run/nut/upsd.pid' to see if previous upsd instance is already running!
Oct 19 02:24:44 N52 nut-server[21031]: listening on ::1 port 3493
Oct 19 02:24:44 N52 nut-server[21031]: listening on 127.0.0.1 port 3493
Oct 19 02:24:44 N52 upsd[21031]: listening on ::1 port 3493
Oct 19 02:24:44 N52 upsd[21031]: listening on 127.0.0.1 port 3493
Oct 19 02:24:44 N52 nut-server[21031]: Connected to UPS [1413031]: usbhid-ups-1413031
Oct 19 02:24:44 N52 upsd[21031]: Connected to UPS [1413031]: usbhid-ups-1413031
Oct 19 02:24:44 N52 upsd[21031]: Running as foreground process, not saving a PID file
Oct 19 02:24:44 N52 nut-server[21031]: Running as foreground process, not saving a PID file
6. 可以看到已经正确连接（Connected to UPS [1413031]: usbhid-ups-1413031），可以关闭ssh终端了，在页面等待一会刷新后，设置中可以发现已经成功识别UPS。
