ECB/FEB and other central banks engage in various programs of quantitative easing. Of course, there is program-to-program variation in terms of details, the essence, however, is to buy dodgy securities/government bonds/etc. from banks. My question is, do you see QE as a form to create capital for the banks? I would answer with a "yes" if asked this question. Because essentially a bank gets money for the securities it sells, that money belong to a bank -> capital.
There are at least three different ways to account for the impact of QE on banks (see The Effects of QE on Bank Lending Behavior) and the one that you cite is known as the "liquidity channel" of QE. As you say, and as per the comment by fesman to your question, taken in isolation, the substitution of risky assets such as MBS for excess reserves should increase regulatory capital ratios, assuming no further actions were taken by the bank. One could also say that, by driving up asset prices in general, QE improves the mark-to-market value of bank equity.
However, in practice, at least in the U.S., it appears that banks do not behave in this way and in fact boosted their holdings of Agency debt and MBS during the QE1-QE3 period (see Charts 2 and 3 in QE and bank balance sheets).
In a sense then, the premise of your question that QE is targeted towards buying securities from banks needs to be re-examined (as the other responses have suggested). In fact, as the change in ownership structures of securities holdings over the QE1-QE3 period demonstrates, U.S. banks were only marginally involved in selling securities held on their balance sheets and were mostly acting as intermediaries for other sellers: hedge funds and the housing GSEs, for example.
I would say "no".
With no quibbles about about the basic premise... Call it "QE", "SMP" (securities' market purchase) or any acronym for any variation thereof, the description of the situation is far from contested here. One can easily, in my view, just look at any central bank's balance sheet to get a feel for the quantum of "magic monetary open operations".
Arguably, one could argue that a trillion's overdraft is not the same thing as buying as buying a trillion's worth of long-term bonds (ie it's the duration effect on fixed-income markets that matters as much as the monetary injection itself?) But this kind of feels like pedants' corner ;-) We had no trillion, then 2, then 4, then 8, now 16 ;-) The "liquidity injection" (call it you prefer, by all means) is real enough.
Except my quibble is that is NOT capital for the banks. In fact, it almost ensures that bank profitability (by crushing NIMs, ie "net interest margins") will not pick up, incentivising any private-sector credit pickup to allow (a private-sector-led) "recovery" scenario.
It's actually bad for the banks. But it is good for borrowers (and bad for savers). The central banks are taking bond yields negative, to remove the incentive for riskless saving. Saving is fine; but it's now become risky, and will become riskier if everyone continues to save too much. So anyone who bought bonds at a positive yield sells them to the central bank, and now must invest/lend to something risky/riskier (unless they fancy negative returns, and deeply negative real returns). That's the point here.
All of this is NOT good for the economics of the traditional banking business model! Which is one reason bank stocks have continued to be dogs despite economic recovery and recapitilisation at "safe" capital levels. Banks will survive now; and safely; just profitlessly so!
Rather the "winners" from all this new capital created are the traditional lenders to government, who have been given a sweetener to lend to somebody riskier, who have given the same sweetener to an investment-grade lender to lend high-yield, who have done the same to a HY guy buy "blue-chip defensive/quality stocks", who have done to a boring conservative stock guy the same to attempt the moonshot on FAANG!
This is all about fostering the "animal spirits", via monetary (but not yet fiscal) channels. Vintage Keynes 101 ;-)