At 1532 GMT, the rand traded at 17.7900 against the dollar, about 1.3% weaker than its previous close.
The dollar recovered slightly against a basket of six major rivals and was last up 0.16% at 103.47 after slipping on Tuesday as less-hawkish-than-expected comments from Federal Reserve Chair Jerome Powell fuelled investor hopes that the central bank may soon ease monetary policy.
South African markets will be turning their focus to the president's speech to parliament, where he is under pressure to offer some solution to address a worsening power crisis.
Daily power cuts since last year have hammered economic growth and are proving a major test for the governing African National Congress, whose support among voters is sliding.
Investors are demanding some leadership, guidance and clarity on the steps being taken to extricate South Africa from the electricity generation crisis, ETM Analytics said in a research note.
On the Johannesburg Stock Exchange, the broader all-share index ended 0.55% higher while the top-40 index closed up 0.73%. It was boosted by the weakened rand as rand-hedged stocks climbed.
Rand-hedged shares such as dual-listed luxury goods retailer Richemont, miner BHP Group and technology investor Prosus make the bulk of their revenue outside South Africa and tend to rise as the currency weakens.
Trade was choppy as investors were cautious to make big bets ahead of Ramaphosa's address as they awaited clues on his plans to tackle crippling power crisis.
Many companies have warned that their margins will be under pressure as they take on additional costs to fire up diesel generators to manage power outages.
The government's benchmark 2030 bond was weaker, with the yield up 1.5 basis points at 9.775%.
(Reporting by Nellie Peyton, Nqobile Dludla and Bhargav Acharya; Editing by Nivedita Bhattacharjee and Angus MacSwan)
