You should apply it every time you install PSP from a MGE UPS PnP detection on a Windows 95/98 system where a previous MGE UPS PnP installation (uninstalled or not) has been done from a different version of PSP.
Note that PnP detection/installation occurs only if the MGE UPS device is removed from Control Panel/System.
After a MGE UPS PnP detection/installation, an MGE INF file is copied in "<Windir>\INF\" directory (Win95) or "<Windir>\INF\OTHER\" directory (Win98).
BUT : PSP files may be different from one version to another (especially true from D version to E version).
For an upgrade, the solutions are :
1) Do not remove the MGE UPS device from Control Panel/System
=> (so that new MGE UPS PnP detection/installation will NOT occur),
=> and run installation program from "Welcome Screen" of SolPac CDROM.
2) If you have already removed the MGE UPS device from Control Panel/System,
=> delete also the MGE INF file,
=> install PSP through PnP detection or through installation
program from "Welcome Screen" of SolPac CDROM.