I think I have solved it - After much scratching of head, and after running many applications / diagnostics to try and establish if anything was wrong with the machine ( after Dell Support staff gave me a bum hint it may be due to firmware or hardware issues ) .. Decided this looks to me like a confused installation of support tools, or maybe a leftover from updates which are not relevant anymore but were left in the system due to support tools updates not being able to remove redundant updates (an old SA Remediation installation struck me as being odd left on the system after SupportAssist had updated to a newer version than the one that needed the remediation update). Long story short - Having uninstalled all Dell Apps, I did a thorough sweep of everything on the C:\ drive and deleted anything I could find to do with Dell in Hidden folders / Temp / Apps / Users / Appdata / Local / Roaming / Program files / Windows etcetera .. Then rebooted. Installed just Dell Update v4 and ran it. It found nothing to update. I guess this is a case of the attention of the company support slowly disolves as a machine runs its life expectancy course, old issues get left behind and incompatabilities are not chased up anymore, drivers and security updates will get left by the wayside for your beloved machine which cost an arm and a leg and eventually you are left with the only option of doing a clean install of the latest windows which will install the most recent generic drivers, and all the original support fluff will be more trouble than it is worth to re-install. Things I didn't re-install : Dell Power Management - Why have such a thing duplicating what Windows already does? SupportAssist and / or any updates which may or may not be Windows 10 compatible / or even relevant / or even named correctly - Am I installing what's listed on the site as a USB or OS recovery plugin but downloads as just a support assist plugin with no mention of USB or OS in the filename??? And what exactly does SupportAssist actually do ( besides try to download updates it can not link to because they do not actually exist O_o ) - Optimize my system?, it all looks very nice but is it really necessary these days when Windows itself slowy optimizes a PCs performance.   I think in future I will stick with just Windows 10 Clean install periodically, and follow up with manual installs of the most recent relevant drivers, and I am reasonably happy at the moment ( at least while the machine is still under warranty ) that Dell Update on its own is all I need to make checking for any important updates a bit more convenient. And just use Windows 10 "Create a Recovery drive" on a USB memory stick for any bad issues.   @ Dell - Your script reading helper could probably have suggested uninstalling all Dell Apps, and weeding out all redundant files they collectively created on my HD as a solution to this issue. Not impressed. The update both SupportAssist and Dell Update were suggesting do not exist for this machine. Even the link in the report in both of them will lead you to a support page which reads something like "The file you are trying to find does not exist" - At least that gave me the clue that maybe the Dell support software is confused . 
As per the title, critical update "Supportassist OS Recovery Tools" v5.3.0.13847 will not install. System = Dell G7 7590   1. Supportassist OS Recovery Tools v5.3.0.13847 is not available in my machines Support page for Driver downloads. There is an older version available (which is already installed, v5.2.1.12926) at    2. Dell Update v4.0.0 tells me there is a critical update to Supportassist OS Recovery Tools, but fails to install Supportassist OS Recovery Tools v5.3.0.13847.   3. Supportassist v3.8.0.108 also notifies me of an Urgent Update Supportassist OS Recovery Tools, but fails to install v5.3.0.13847.     Steps taken to try and resolve: Uninstalled and re-installed latest versions of Supportassist and Dell Update Rebooted Tried again with both tools. Both failed again.   I do not have any large Anti-Malware suites installed, I only use Windows Defender. My firewall is not preventing any of the support tools from connecting. I use Quad9 9.9.9.9 as Primary DNS server, and Cloudflare 1.1.1.1 as secondary server (to assist in helping us not be linked to bad sites / links), and otherwise do not to use naughty / warez sites, nor download third party tools with potential bad installers and hidden / obfuscated agendas.   I believe there is a recent issue where anti-malware is locking file downloads preventing whatever is downloading them from using them (such as Google Chrome downloading fav icons and not being able to update them, and similarly any direct file downloads Chrome has adapted a bit of a kludge fix recently, whereby any file downloading which immediately becomes locked by the system, Chrome now just retries over and over until the file being downloaded becomes unlocked, so in my case Windows Defender is also part of that particular problem, I have seen Chrome retrying many times to grab your own downloadable drivers (and due to Windows Defender being so well embedded in Windows 10 I would not be happy to disable it or even know where to start with its many services, getting it back up and running may prove too problematic so I am not willing to go there if it comes up as a troubleshooting step) .. .. Could this be part of the problem for Supportassist and Dell update? Also why is the update to Supportassist OS Recovery tools not available on the machine specific drivers download page?
Dell G7 7590 - Supportassist OS Recovery Tools v5.3.0.13847 will not install