There's this thing called the laws of physics. The output rails of an ATX PSU have massive amounts of capacitance on them. This means that the output voltage simply can't change that fast.
Dunno what you mean with "massive amounts of capacitance" but if you take a look to modern topolopy ATX PSUs where a single 12V bar supply several
very high frequency DC/DC converters to provide +5V, +3V3 and so on, you can find
ceramic capacitor and/or small low ESR electrolytic in output stages, sure not "massive" values (take a look to Corsair AX series, for instance).
The voltage ripple/drop that you can find on those outputs under medium/heavy load could be quite nasty and very far to be monitored with 87V peak capabilities, an utterly wrong instrument to keep in account in this scenario.
I could agree that with linear PSU it would come in handy in absence of a DSO, but nowaday everyone has at least one
Just out of curiosity, have you ever used an 87V?
I used a Fluke 189 for several years for ordinary task, the lab where i was before (yes, the employer was paying the bill) had a bunch of them, some failed, mine lost buzzer function after a while.
Despite so i liked it, but you could understand why i do not consider them "foolproof".
What if my 869S fails out of warranty ?
Simple, i'll buy another one (or something else, if available), still saving money against a single Fluke 87V and taking advantage with :
- double thermocouple reading
- double display
- additional resolution digit
- pc interface
all things that i care for .
But considering that my piece of cr@p V&A VA38 still works after six years of continuos job, with its creaky & scratchy case, i will dare to say that this one has the potential to last waaay more.
I do not have any personal interest to push BRYMEN products, i only think that for the price they are a smart choice for hobbiest, while professionals and companies, being able to deduct equipments purchases from taxes, will continue to be the preferred Fluke's customers.