Pete the Planner's website appears very commercially oriented, and appears to only have podcasts to explain his Power Percentage (I can't listen at work and would rather read something quickly). His petesmoneyschool website requires you to create a login to glean any info about his Power Percentage. With a little googling, I found a usatoday article of his, and the outline is basically this:
add up any retirement savings, company match, extra long term savings, college savings, mortgage principle paydown, and other credit card and student loan debt reduction payments (monthly or yearly), and divide by your total gross income (monthly or yearly), and you get a percentage.
I think as you said, this is pretty basic stuff, and I don't see much difference between this and a MMM approach. I guess MMM's slight twist is to envision what you will actually need in FIRE, and then use that as the denominator, rather than your actual income. And has been pointed out many times, if you are using income as a denominator, especially if you have high income, you might be biased towards making fewer changes. So I'm not convinced that the Power Percentage is necessarily more conservative. Yes it will tend to give you a lower percentage than MMM's approach in many circumstances, but it also implicitly argues for keeping the status quo of spending in some respects, after all if you are spending a 100k a year, and your PP is above 35% and therefore doing an excellent job on his scale, is that person or family really more immune to financial shocks compared to someone who has actively tallied up their true needs and is measuring their financial picture against whether they can cover those or not?