There are so many systematic withdrawal methods out there, but they do fall into two major categories.
Fixed amount each year (adjusted for inflation)
Variable amount (% withdrawn may be fixed or increasing over time like VPW, but whether the withdrawals keep up with inflation is totally dependent on your portfolio's returns)
And of course you can create a hybrid between the two major categories.
In the variable category, there are many methods out there to smooth year-to-year withdrawals. For example: Scott Burns and others have mentioned taking some fixed percentage of your portfolio out each year OR 90% of the previous year's withdrawal, whichever is largest. The 90% (or whatever % you're comfortable with) limits how far your annual withdrawals can drop relative to the previous year's withdrawal during a down market.
Back to the 4% "rule", the studies show that over history most of the time you could have withdrawn more than 4% - meaning that most of the time in history, you'll croak leaving a large sum behind. Fine if you want to leave some behind. Not so fine if you wished you could have used that during retirement.
Enter several methods that help you take advantage if you didn't happen to retire at the worst time in history.
1. Kitces Ratcheting described here:
https://www.kitces.com/blog/the-rat...l-rate-a-more-dominant-version-of-the-4-rule/
Shows you a method to increase your withdrawals over time (beyond inflation) if your portfolio is still continuing to grow after several years of withdrawals.
2. And oldy but goody and one of my favorites: Gummy's sensible withdrawals described here:
sensible withdrawals
If you can live on less than the amount described in the 4% rule, this is a method that allows you to withdraw some percentage of the extra returns during years when your portfolio has grown even after taking your withdrawal and inflation into account. I tend to like it because it's sort of like a bonus at work. You (your portfolio) does well, you get a bonus, otherwise, no bonus. I also like it because, statistically, when a bonus happens, it tends to happen earlier in retirement instead of later - meaning that you might have bonuses earlier in retirement when you still want to travel, etc.
As mentioned, the systematic withdrawal methods are endless and one-size definitely does not fit all.