Now back on the sticker topic. I looked it up and came across something interesting - that these may actually be illegal since 1975.
Not exactly, it literally comes down to two words
( I AM DEFINITELY NOT A LAWYER ):
15 U.S. Code § 2304(c) wrote:
The performance of the duties under subsection (a) shall not be required of the warrantor if he can show that the defect, malfunction, or failure of any warranted consumer product to conform with a written warranty, was caused by damage (not resulting from defect or malfunction) while in the possession of the consumer, or unreasonable use (including failure to provide reasonable and necessary maintenance).
So, is opening a PSU to clean it unreasonable?
Well, I would argue yes. I've been building computers for like ~15 years and I've never once seen fit to open up a PSU. As you even acknowledge, it is potentially dangerous
to do that.
So, where does this idea come from? Well, it's because Magnuson-Moss is intended to prevent abuses of the "warranty sticker" concept
, like a theoretical situation in which a car manufacturer slaps one on an entire car and then forces you to pay $1000 for an oil change because you can only get that done at their "certified repair" centers or your warranty is worthless. This law is intended to supercede that kind of gambit entirely, because it doesn't matter what people signed or what the manufacturer provided as a warranty, you just can't do that and then rely on inviolable legal principles about "contracts must be kept" or "buyer beware explicitly stated warranties" etc...
Because, quite obviously, oil changes are "reasonable and necessary maintenance" as the statute literally says, to the point where if you (the consumer) DON'T have them performed, well, you've also voided the warranty through gross neglect on the other side. It's like the mirror opposite scenario, in fact.
Also, the act is remedy-oriented: it works by preserving the consumer's right to file a lawsuit and obtain relief (i.e. GIVE MY DARN WARRANTY YOU SCHEMING HUCKSTERS), not by directly constraining the behavior of manufacturers. In other words, it's not that warranty void stickers are illegal, it's just that they aren't necessarily legally binding.
Generally, these sorts of things (consumer remedies) never boil down into simple statutes. Too much interplay, too many factors. The statutes just establish basic principles, not absolute decrees, and it's all case law from that point forward. ABUNDANT case law that is almost entirely derived from a mere handful of words.