Now that you mention this… a friend did help him fit some “lights” in the pc that constantly glows and changes colour, even when the PC is of.
It looks like one of the components has its own light built in, and the two fans fitted to the case also illuminates. But I don’t think these are too power hungry.
That should not be a problem at all…
These days they are all LED so don’t worry about them.
@Swartkat - get a cheap UPS.
Or even better … get a UPS that someone has thrown away, replace the 12v 7ah battery, and it works again … or leave the 12v 7ah and go 12v 6ah lithium teeny weeny bank. 
Serves two purposes:
I’m seriously considering this yes as added protection.
And I’ve seen cases where it causes a shutdown because it turns out to be worse than the upstream UPS 
I absolutely agree that a good quality dedicated UPS might still be a good idea. It just doesn’t always improve the situation. And that little 7Ah battery has a habit of failing when you least expect it.
Yeah, I’ve seen that … but we don’t buy that cheap anymore?
A good quality CS3 12v 9ah should last about 3-5 years easily. But as with ANY Lead Acid battery, you abuse it, they all have a tendency to develop a habit of failing when you least expect it. 
If you have a pure sinewave inverter … like say a Victron … before the modified/square sine wave UPS, it will keep that PC/TV/Sound System on, and it has more protections built-in than say an i.e. Victron inverter. 
On my 1kva 24v APC UPS, this is it’s new battery bank …
16 x 6ah 3.2v lithium cells in series, 2 banks in parallel = 24v 12ah bank
Close as damn in price compared to 4 x 9ah CS3 batteries, that is, until 5 years from now. Then the lithium bank, ito price, wins hands down.
Should have gone for a bigger 24v BMS, but the price was not worth it, as the small ones do the job with panache.
EDIT: And do NOT connect said 1kva APC UPS to a 500va Multiplus … it does not work. 
Connected to a 5kva Multiplus II, THAT is ok…
En daar slaat die beurtkrag ons weer.
Dit voel so lekker om 'n email te kry om te sê “hey! gaan kyk gou wat aangaan, die krag in jou huis is af!”
En dan gaan kyk jy en sien dat jou inverter nie vir jou gelieg het nie. En jy het nie eers daarvan geweet nie, lol. 
Rekenaar is ook heel happy op sy nuwe muurprop.
Some more feedback here.
It turns out, the new wall socket that we plug the computer in now is also on the same line that the fridges are. So the computer still shuts down when the power dips or grid is lost.
So, having regard to all the advice above, it further appeared that the power supply was acting up - tired capacitors maybe as it we started experiencing issues on the ram, motherboard, hard drive etc.
So we replaced the 700W psu with a new 750psu.
Computer still shuts down when grid is lost.
Then, we borrow UPS from a friend.
It is over 10 years old but the batteries (2 x 7Ah’s) still seems fine judging by my tests which involved having my 50W two way radio connected to one at a time, and transmitting on it for a minute or so and leaving it on for about 2 hours at a time for each battery.
I know this lifespan is unheard of for these gate motor sealed lead acids but still.
Oh yes and it is a 600W unit
So I have been told that it is very seldom that the PC would run at full capacity (750W) and is more likely to be working around 300-400W under normal conditions.
But… even this 600W Ups does not stop the PC from shutting down??? I means surely it could provide enough juice for just that split second it takes the Multiplus to kick in?
Could something else on the Ups be wrong and how would I test for it?
600w or 600va i.e. like 400w?
If the batts are old, when it gets a spike from taking over, the batts could drop off a cliff causing the shutdown of the UPS too.
Or, spitballing, there is a problem on that circuit.
The specs on it says 1000Va / 600W
Hi, did this ever come to a happy ending?
No I haven’t figured out what the issue is on the UPS and I have no idea on how to test for the issue it clearly has.
So it is lying here gathering dust until we are able to buy a new one.
